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These are the user uploaded subtitles that are being translated: 1 00:00:01,000 --> 00:00:05,480 Notre-Dame de Paris, a treasured icon of Gothic architecture 2 00:00:05,480 --> 00:00:08,300 and medieval engineering. 3 00:00:08,300 --> 00:00:09,680 Built from glass, 4 00:00:09,680 --> 00:00:10,840 stone 5 00:00:10,840 --> 00:00:14,400 and timber over the course of two centuries, 6 00:00:14,400 --> 00:00:17,400 it's one of the world's greatest cathedrals. 7 00:00:18,300 --> 00:00:21,320 Notre-Dame is one of humanity's greatest 8 00:00:21,320 --> 00:00:23,520 artistic and architectural achievements. 9 00:00:23,520 --> 00:00:26,840 This epic 90-metre-tall symbol has stood 10 00:00:26,840 --> 00:00:32,160 at the heart of French culture and society for 850 years. 11 00:00:32,160 --> 00:00:34,360 SPEAKS IN FRENCH 12 00:00:38,360 --> 00:00:41,400 But on 15th April 2019, 13 00:00:41,400 --> 00:00:43,040 disaster strikes. 14 00:00:43,040 --> 00:00:45,760 PEOPLE SCREAM AND SHOUT 15 00:00:45,760 --> 00:00:50,320 A massive fire rages out of control and tears through the cathedral... 16 00:00:53,040 --> 00:00:54,560 ..leaving it in ruins. 17 00:00:58,200 --> 00:01:02,280 Now, a team of master craftspeople and elite engineers 18 00:01:02,280 --> 00:01:05,600 battle to save this fragile structure 19 00:01:05,600 --> 00:01:08,440 from a catastrophic collapse. 20 00:01:10,120 --> 00:01:11,840 SHE SPEAKS IN FRENCH 21 00:01:14,880 --> 00:01:17,880 Out of tragedy is born opportunity... 22 00:01:17,880 --> 00:01:19,120 Oh! 23 00:01:22,920 --> 00:01:27,280 ..to solve archaeological mysteries and understand the very fabric 24 00:01:27,280 --> 00:01:30,760 of this medieval megastructure like never before. 25 00:01:30,760 --> 00:01:33,760 We can identify each chemical element. 26 00:01:33,760 --> 00:01:36,280 Yes, it is important information. 27 00:01:36,280 --> 00:01:40,320 For the last year, our cameras have had unique access 28 00:01:40,320 --> 00:01:43,800 to follow teams inside Notre-Dame. 29 00:01:43,800 --> 00:01:49,600 Can they decode clues from the past and use pioneering technology 30 00:01:49,600 --> 00:01:52,040 to rebuild this historic landmark? 31 00:01:53,760 --> 00:01:58,680 This is the inside story of the first year in the race 32 00:01:58,680 --> 00:02:00,840 to save Notre-Dame Cathedral. 33 00:02:10,600 --> 00:02:13,240 The Cathedral of Notre-Dame de Paris, 34 00:02:13,240 --> 00:02:16,480 an 850-year-old Gothic wonder. 35 00:02:18,800 --> 00:02:20,760 It's the heart of France. 36 00:02:20,760 --> 00:02:24,440 Roads were traditionally measured from this iconic structure. 37 00:02:26,440 --> 00:02:28,400 There was a continuation, 38 00:02:28,400 --> 00:02:32,120 a historical continuation from the Middle Ages to nowadays. 39 00:02:32,120 --> 00:02:38,240 And it's very important to build a kind of identity. 40 00:02:38,240 --> 00:02:42,560 Notre-Dame is one of the monuments which achieved this identity. 41 00:02:44,520 --> 00:02:46,600 For Christians, it's a place of worship, right? 42 00:02:46,600 --> 00:02:48,800 And for those of us with different beliefs, 43 00:02:48,800 --> 00:02:51,880 it's one of...just this incredible artistic and historical landmark. 44 00:02:51,880 --> 00:02:53,680 You've had coronations there, 45 00:02:53,680 --> 00:02:56,360 you've had the crowning of Napoleon and King Henry 46 00:02:56,360 --> 00:02:58,960 and there's just so much attached to the cathedral. 47 00:02:58,960 --> 00:03:02,000 But Notre-Dame is much more than that. 48 00:03:02,000 --> 00:03:05,360 It's also the pinnacle of medieval engineering. 49 00:03:06,880 --> 00:03:10,480 The cathedral can hold 9,000 worshippers 50 00:03:10,480 --> 00:03:12,640 and its 33-metre-tall walls 51 00:03:12,640 --> 00:03:17,200 contain more than 3,000 square metres of stained glass. 52 00:03:18,680 --> 00:03:22,520 The ceiling is a series of domed Gothic vaults 53 00:03:22,520 --> 00:03:24,840 that hold up the cathedral from the inside. 54 00:03:26,160 --> 00:03:31,280 A complex 500-tonne web of timber forms a cross-shaped roof 55 00:03:31,280 --> 00:03:34,600 topped with 1,300 lead tiles... 56 00:03:36,480 --> 00:03:38,960 ..and a 90-metre-tall central spire. 57 00:03:41,600 --> 00:03:45,320 Wrapped around the church are 28 flying buttresses, 58 00:03:45,320 --> 00:03:49,000 limestone arches that brace the walls from the outside... 59 00:03:50,480 --> 00:03:54,400 ..and at the front, two mighty towers, 60 00:03:54,400 --> 00:03:57,560 with ten massive bronze bells inside, 61 00:03:57,560 --> 00:04:02,720 soar over 68 metres into the sky over Paris. 62 00:04:02,720 --> 00:04:05,280 The construction took many generations. 63 00:04:06,400 --> 00:04:09,600 Architecture was not learned at the university. 64 00:04:09,600 --> 00:04:14,520 So, the architects and all workers learned mostly onsite. 65 00:04:15,600 --> 00:04:17,640 Along the way, there were many setbacks. 66 00:04:17,640 --> 00:04:21,600 In 1789, at the height of the French Revolution, 67 00:04:21,600 --> 00:04:25,480 anti-Catholic forces destroy parts of the cathedral. 68 00:04:25,480 --> 00:04:30,760 A newly secular France leaves Notre-Dame in a state of neglect. 69 00:04:30,760 --> 00:04:35,600 But when Victor Hugo writes The Hunchback Of Notre-Dame in 1831, 70 00:04:35,600 --> 00:04:39,560 it sparks a £170 million restoration 71 00:04:39,560 --> 00:04:42,600 that tops up the cathedral with a new roof 72 00:04:42,600 --> 00:04:46,120 and a 750-tonne timber and lead spire. 73 00:04:50,400 --> 00:04:54,440 And periodic renovations continue to this day. 74 00:04:54,440 --> 00:05:00,840 On 15th April 2019, Notre-Dame is wrapped in 500 tonnes of scaffolding 75 00:05:00,840 --> 00:05:05,280 as the cathedral begins a £5 million operation 76 00:05:05,280 --> 00:05:07,160 to shore up the spire. 77 00:05:07,160 --> 00:05:09,360 THEY SPEAK IN FRENCH 78 00:05:12,360 --> 00:05:15,360 Notre-Dame's rector, Monsignor Patrick Chauvet, 79 00:05:15,360 --> 00:05:17,320 has finished evening worship. 80 00:05:17,320 --> 00:05:20,520 His world is about to be turned upside down. 81 00:05:20,520 --> 00:05:23,160 HE SPEAKS IN FRENCH 82 00:05:42,560 --> 00:05:48,160 At 6.18pm, a sensor detects smoke in the medieval roof timbers. 83 00:05:48,160 --> 00:05:51,680 The system sends a coded fire alert to the security team. 84 00:05:52,800 --> 00:05:55,160 Instead of heading straight for the roof, 85 00:05:55,160 --> 00:05:58,720 a guard is dispatched to the sacristy building nearby 86 00:05:58,720 --> 00:06:00,120 to check for a fire. 87 00:06:00,120 --> 00:06:01,840 But he finds nothing. 88 00:06:01,840 --> 00:06:04,280 He climbs up into the church attic. 89 00:06:04,280 --> 00:06:07,880 But by the time he gets there, he's too late. 90 00:06:07,880 --> 00:06:11,520 The fire has been burning for almost 30 minutes 91 00:06:11,520 --> 00:06:14,160 and spread across the roof. 92 00:06:14,160 --> 00:06:16,320 SIREN BLARES 93 00:06:18,200 --> 00:06:21,640 And there was this horrifyingly huge plume of smoke 94 00:06:21,640 --> 00:06:23,480 billowing up out of it. 95 00:06:23,480 --> 00:06:26,400 It was surreal. I'd never seen anything like that before. 96 00:06:27,480 --> 00:06:30,400 You saw the fire trucks come up alongside the cathedral 97 00:06:30,400 --> 00:06:32,800 and ladders went up and the hoses came out. 98 00:06:32,800 --> 00:06:34,280 You could see that the ladders 99 00:06:34,280 --> 00:06:36,320 were just too small for a building of this size. 100 00:06:36,320 --> 00:06:38,840 And the hoses were not nearly big enough for this kind of blaze. 101 00:06:38,840 --> 00:06:40,360 It was tragic. 102 00:06:40,360 --> 00:06:43,200 The resources that were available were not going to be what was needed 103 00:06:43,200 --> 00:06:44,800 to bring this thing under control. 104 00:06:46,040 --> 00:06:48,080 A lot of us realised that this fire 105 00:06:48,080 --> 00:06:50,240 was just going to ravage the cathedral. 106 00:06:50,240 --> 00:06:52,480 SPEAKS IN FRENCH 107 00:06:57,960 --> 00:07:01,160 A delay in responding to a fire of this nature 108 00:07:01,160 --> 00:07:02,720 is absolutely critical. 109 00:07:02,720 --> 00:07:05,880 A small fire burning locally is a very different thing 110 00:07:05,880 --> 00:07:09,880 than ten minutes later when all of the timber elements are involved. 111 00:07:09,880 --> 00:07:11,960 So, in a situation like this, 112 00:07:11,960 --> 00:07:14,480 five, ten, 30 minutes can make all the difference. 113 00:07:15,560 --> 00:07:18,200 This delay will have huge repercussions. 114 00:07:18,200 --> 00:07:21,000 As firefighters arrive on scene, 115 00:07:21,000 --> 00:07:24,520 so does one of France's chief architects of historic monuments, 116 00:07:24,520 --> 00:07:26,080 Remi Fromont. 117 00:07:26,080 --> 00:07:28,080 HE SPEAKS IN FRENCH 118 00:07:31,760 --> 00:07:35,080 As the inferno rages at the top of the cathedral, 119 00:07:35,080 --> 00:07:38,640 Remi risks his life to venture inside with the firefighters. 120 00:07:50,880 --> 00:07:54,280 Within minutes, the firefighters are pumping tonnes of water 121 00:07:54,280 --> 00:07:57,360 into the attic space, but it's not working. 122 00:07:58,600 --> 00:08:03,920 To the horror of the growing crowd, the fire engulfs the famous spire. 123 00:08:05,680 --> 00:08:07,720 The world watches helplessly 124 00:08:07,720 --> 00:08:12,240 as the 750-tonne oak and lead masterpiece gives way. 125 00:08:14,800 --> 00:08:16,360 Oh, my God. 126 00:08:16,360 --> 00:08:17,880 Oh, my God, that is awful. 127 00:08:21,280 --> 00:08:23,960 When the spire fell into the roof, 128 00:08:23,960 --> 00:08:26,600 an additional ventilation will have caused 129 00:08:26,600 --> 00:08:30,080 more oxygen-rich air to be sucked in at the bottom of the compartment. 130 00:08:30,080 --> 00:08:33,920 That influx of oxygen could have caused an increase 131 00:08:33,920 --> 00:08:36,960 in the severity of the fire within Notre-Dame. 132 00:08:49,120 --> 00:08:51,640 It was just devastating to watch. 133 00:08:51,640 --> 00:08:54,360 We were suddenly really aware that...of how easily 134 00:08:54,360 --> 00:08:56,160 this whole thing could come down. 135 00:08:57,920 --> 00:09:00,320 90 minutes after the fire begins, 136 00:09:00,320 --> 00:09:03,160 the entire roof of the cathedral is ablaze. 137 00:09:06,320 --> 00:09:08,920 Inside, it's become even more dangerous 138 00:09:08,920 --> 00:09:10,880 for Remi and the firefighters. 139 00:09:10,880 --> 00:09:13,920 Getting this fire under control looks impossible. 140 00:09:25,280 --> 00:09:27,560 A south-easterly wind picks up 141 00:09:27,560 --> 00:09:30,920 and pushes the blaze towards the famous bell towers. 142 00:09:36,560 --> 00:09:41,000 Inside the ingeniously engineered 13th-century north tower, 143 00:09:41,000 --> 00:09:44,680 a scaffold of wooden beams holds eight bells, 144 00:09:44,680 --> 00:09:48,040 the biggest weighing more than four tonnes. 145 00:09:48,040 --> 00:09:49,880 If the beams burn through, 146 00:09:49,880 --> 00:09:52,240 they'll trigger a fatal chain reaction. 147 00:09:53,960 --> 00:09:56,640 The bells will fall like wrecking balls 148 00:09:56,640 --> 00:09:58,880 and destroy the tower's wooden backbone. 149 00:10:01,800 --> 00:10:07,000 If the tower falls, it could trigger a deadly domino effect 150 00:10:07,000 --> 00:10:09,280 that brings down the entire cathedral. 151 00:10:14,720 --> 00:10:17,200 To avert this catastrophic collapse, 152 00:10:17,200 --> 00:10:21,760 the firefighters have no option but to venture deeper inside. 153 00:10:28,880 --> 00:10:31,520 REMI: 154 00:10:46,160 --> 00:10:48,080 To douse the fire on the roof, 155 00:10:48,080 --> 00:10:50,720 firefighters pump water from the River Seine 156 00:10:50,720 --> 00:10:53,760 and feed it to fire trucks around the cathedral. 157 00:10:53,760 --> 00:10:56,280 But to stop the towers collapsing, 158 00:10:56,280 --> 00:10:59,440 they must send a team into the burning structure. 159 00:10:59,440 --> 00:11:00,920 Their mission - 160 00:11:00,920 --> 00:11:03,080 drop hoses in between the towers 161 00:11:03,080 --> 00:11:05,640 and fight the fire spreading from the roof. 162 00:11:05,640 --> 00:11:08,080 But the steady wind doesn't let up. 163 00:11:08,080 --> 00:11:11,680 And despite their efforts, the timber frame holding the bells 164 00:11:11,680 --> 00:11:15,640 has caught fire and could trigger the destruction of the cathedral 165 00:11:15,640 --> 00:11:17,240 at any moment. 166 00:11:17,240 --> 00:11:20,520 So, the team must drag their hoses to the top of the tower 167 00:11:20,520 --> 00:11:24,240 and soak the timber frame to prevent the unthinkable. 168 00:11:31,640 --> 00:11:35,280 Throughout the night, the fate of Notre-Dame hangs in the balance. 169 00:11:36,440 --> 00:11:39,760 Eventually, the firefighters get the upper hand. 170 00:11:40,760 --> 00:11:42,680 The flames have been beaten back 171 00:11:42,680 --> 00:11:45,840 and only glowing embers light up the night sky. 172 00:11:47,000 --> 00:11:48,800 Nobody knows how the fire started. 173 00:11:49,800 --> 00:11:51,880 An investigation begins. 174 00:11:51,880 --> 00:11:54,800 But for now, the urgent question - 175 00:11:54,800 --> 00:11:59,520 how damaged is the structure and can it ever be rebuilt? 176 00:12:00,880 --> 00:12:04,560 President Macron pledges to restore the cathedral in five years. 177 00:12:04,560 --> 00:12:06,320 HE SPEAKS IN FRENCH 178 00:12:12,080 --> 00:12:14,480 PEOPLE SING TOGETHER 179 00:12:14,480 --> 00:12:16,720 The world keeps vigil for Notre-Dame. 180 00:12:24,840 --> 00:12:28,480 Daylight reveals the full extent of the terrible destruction 181 00:12:28,480 --> 00:12:30,200 wrought by the fire. 182 00:12:31,600 --> 00:12:34,520 The oak roof and spire are completely destroyed. 183 00:12:36,160 --> 00:12:39,760 Toxic lead that covered the roof has been sprayed into the air, 184 00:12:39,760 --> 00:12:41,480 contaminating the site. 185 00:12:43,440 --> 00:12:46,280 Burned roof timbers cover the vaulting. 186 00:12:46,280 --> 00:12:50,680 Three gaping holes in the stone vaults weaken the entire structure. 187 00:12:50,680 --> 00:12:54,880 And the 500-tonne scorched carcass of scaffolding 188 00:12:54,880 --> 00:12:56,960 could collapse at any moment... 189 00:12:57,960 --> 00:13:00,280 ..something unthinkable to those 190 00:13:00,280 --> 00:13:04,040 tasked with preserving France's rich cultural heritage. 191 00:13:04,040 --> 00:13:06,600 SPEAKS IN FRENCH 192 00:13:09,760 --> 00:13:13,600 Philippe Villeneuve is in charge of historic monuments in France. 193 00:13:13,600 --> 00:13:17,920 This is the cathedral that inspired him to become an architect. 194 00:13:34,160 --> 00:13:39,160 Since 2013, Philippe has been in charge of conserving Notre-Dame. 195 00:13:49,960 --> 00:13:53,840 The stricken cathedral is a giant house of cards. 196 00:13:53,840 --> 00:13:57,480 If the stone vaulting collapses, the weight of the buttresses 197 00:13:57,480 --> 00:14:02,680 will push in the 33-metre-high walls and Notre-Dame will be no more. 198 00:14:10,640 --> 00:14:13,600 So, Philippe assembles a rapid response team, 199 00:14:13,600 --> 00:14:16,840 dozens of engineers, architects and scientists. 200 00:14:17,960 --> 00:14:21,840 Their task is to prevent a total collapse of the cathedral. 201 00:14:32,840 --> 00:14:35,280 It's not only a difficult job, 202 00:14:35,280 --> 00:14:36,880 it's also hazardous. 203 00:14:39,040 --> 00:14:42,440 The crumbling stone vaults and twisted scaffolding 204 00:14:42,440 --> 00:14:44,280 make even venturing inside 205 00:14:44,280 --> 00:14:46,840 to investigate the stability of the structure 206 00:14:46,840 --> 00:14:49,480 extremely dangerous. 207 00:14:49,480 --> 00:14:51,120 SHE SPEAKS IN FRENCH 208 00:15:02,280 --> 00:15:04,320 ALARM BLARES 209 00:15:04,320 --> 00:15:06,480 SHE SPEAKS IN ENGLISH 210 00:15:10,520 --> 00:15:12,440 Motion sensors are installed 211 00:15:12,440 --> 00:15:14,960 in the melted jumble of scaffolding overhead. 212 00:15:14,960 --> 00:15:17,400 These can be triggered by gusts of wind 213 00:15:17,400 --> 00:15:20,120 or signal a full-scale collapse. 214 00:15:32,480 --> 00:15:36,680 There are evacuations like this each week that slow progress. 215 00:16:03,840 --> 00:16:07,400 To avert a catastrophic collapse, engineers could build 216 00:16:07,400 --> 00:16:11,280 a steel skeleton inside the nave to brace the walls. 217 00:16:12,760 --> 00:16:15,040 Then, even if the vaulting caves in, 218 00:16:15,040 --> 00:16:18,040 the walls of Notre-Dame would stay standing. 219 00:16:19,480 --> 00:16:22,880 But it's far too dangerous for workers to erect steelwork 220 00:16:22,880 --> 00:16:24,760 beneath the compromised structure. 221 00:16:31,040 --> 00:16:33,760 So, instead of bracing the walls from the inside, 222 00:16:33,760 --> 00:16:39,040 the team will build timber frames under the buttresses outside. 223 00:16:39,040 --> 00:16:41,040 Now, if the vaulting does fall in, 224 00:16:41,040 --> 00:16:43,760 the buttresses can't push on the walls 225 00:16:43,760 --> 00:16:45,880 and they won't come tumbling down. 226 00:16:48,240 --> 00:16:50,360 THEY SPEAK IN FRENCH 227 00:17:03,640 --> 00:17:07,400 Workers at this specialised factory race to cut and assemble 228 00:17:07,400 --> 00:17:10,760 around 225 tonnes of timber 229 00:17:10,760 --> 00:17:13,320 to create the massive supports 230 00:17:13,320 --> 00:17:15,760 Philippe's team needs to prop up the vaults. 231 00:17:15,760 --> 00:17:18,760 It's critical each support fits perfectly 232 00:17:18,760 --> 00:17:22,160 beneath each flying buttress to hold its weight. 233 00:17:26,440 --> 00:17:30,760 Working around and inside this space is a logistical nightmare. 234 00:17:30,760 --> 00:17:34,920 200 tonnes of lead cladding covered the cathedral roof. 235 00:17:36,000 --> 00:17:38,520 This was mostly melted during the fire 236 00:17:38,520 --> 00:17:41,760 and now toxic lead dust covers every surface. 237 00:17:41,760 --> 00:17:45,040 The work site is highly contaminated. 238 00:17:46,200 --> 00:17:47,920 Until the site is cleaned, 239 00:17:47,920 --> 00:17:50,800 team members must wear full protective clothing 240 00:17:50,800 --> 00:17:53,760 to pass into the contaminated zone. 241 00:17:53,760 --> 00:17:57,920 When leaving site, they undress, 242 00:17:57,920 --> 00:18:03,720 discard all clothing, carefully wash equipment, then shower themselves. 243 00:18:05,280 --> 00:18:08,080 Only then can they go back to the clean area, 244 00:18:08,080 --> 00:18:10,440 even for a lunch break. 245 00:18:26,040 --> 00:18:31,120 But finally, five months later, all 28 flying buttresses 246 00:18:31,120 --> 00:18:33,680 are locked in place and the walls are safe. 247 00:18:33,680 --> 00:18:36,400 Now, they can turn to the next challenge - 248 00:18:36,400 --> 00:18:38,960 secure the melted massive scaffolding 249 00:18:38,960 --> 00:18:41,520 that hangs precariously over the cathedral. 250 00:18:43,080 --> 00:18:46,320 The scaffold weighs more than a jumbo jet 251 00:18:46,320 --> 00:18:49,400 and only rests on four spindly legs. 252 00:18:50,680 --> 00:18:54,480 The team plans to wrap three massive steel lattice beams around it 253 00:18:54,480 --> 00:18:56,880 to tie the fragile upper parts together. 254 00:19:00,160 --> 00:19:03,200 Then they'll build more scaffolding either side 255 00:19:03,200 --> 00:19:05,040 and lay steel beams across it. 256 00:19:08,240 --> 00:19:12,080 This way, workers can get inside the stricken scaffolding 257 00:19:12,080 --> 00:19:14,880 to help cut off its 50,000 steel poles. 258 00:19:16,000 --> 00:19:18,000 A truly herculean task. 259 00:19:22,040 --> 00:19:25,920 Only then can the team put up a temporary roof 260 00:19:25,920 --> 00:19:29,400 to protect them from the elements while they rebuild Notre-Dame. 261 00:19:39,800 --> 00:19:43,240 While engineers gear up to remove the scaffolding, 262 00:19:43,240 --> 00:19:46,520 architect Remi Fromont and Livio De Luca 263 00:19:46,520 --> 00:19:48,880 begin a ground-breaking project 264 00:19:48,880 --> 00:19:53,160 that will combine the investigative work with new scientific analysis. 265 00:19:55,680 --> 00:19:59,520 Their ambition is to create a data-rich model of Notre-Dame, 266 00:19:59,520 --> 00:20:01,840 a digital twin. 267 00:20:01,840 --> 00:20:07,600 The digital twin will embed not only the geometric structure, 268 00:20:07,600 --> 00:20:10,400 or the visual appearance of the cathedral, 269 00:20:10,400 --> 00:20:15,920 but also all the scientific data coming from studies. 270 00:20:15,920 --> 00:20:19,360 For example, you can click on a stone in the vault 271 00:20:19,360 --> 00:20:24,240 and access to all the information about its physical properties 272 00:20:24,240 --> 00:20:26,040 such as the provenance, 273 00:20:26,040 --> 00:20:30,560 but also the mechanical behaviour within the entire structure. 274 00:20:31,960 --> 00:20:38,080 This 3-D dynamic map will show every stone, timber and iron nail 275 00:20:38,080 --> 00:20:42,920 in the structure across time from the 12th century 276 00:20:42,920 --> 00:20:44,760 to the present day. 277 00:20:44,760 --> 00:20:48,400 This is an unprecedented project. 278 00:20:48,400 --> 00:20:52,080 The ambition is to collect all the information 279 00:20:52,080 --> 00:20:54,720 from the past to pass it to the future. 280 00:20:55,840 --> 00:20:57,760 There's very little first-hand information 281 00:20:57,760 --> 00:20:59,400 about the construction of Notre-Dame, 282 00:20:59,400 --> 00:21:01,160 or the craftspeople who built it. 283 00:21:03,520 --> 00:21:07,480 In the wake of the fire, new studies of the cathedral's materials 284 00:21:07,480 --> 00:21:09,120 could unlock these secrets. 285 00:21:10,880 --> 00:21:14,200 This new data captured in the digital twin 286 00:21:14,200 --> 00:21:17,920 will provide a blueprint for the restoration and rebuild. 287 00:21:23,280 --> 00:21:27,400 Inside Notre-Dame, scientists begin to gather data 288 00:21:27,400 --> 00:21:32,400 and investigate the damage to treasured statues, murals and windows. 289 00:21:37,360 --> 00:21:42,160 The cathedral's most fragile wonder, its stained glass, 290 00:21:42,160 --> 00:21:44,360 dates back to the 13th century. 291 00:21:45,520 --> 00:21:50,360 36 windows circle the lower level, 42 around the middle level 292 00:21:50,360 --> 00:21:52,760 and 43 around the upper level. 293 00:21:55,120 --> 00:22:00,360 The three famous rose windows span up to 13 metres in diameter 294 00:22:00,360 --> 00:22:05,200 and are made up of over 1,100 panels of beautiful stained glass. 295 00:22:06,560 --> 00:22:11,160 But the intense heat from the fire that melted the cathedral's lead-covered roof 296 00:22:11,160 --> 00:22:15,120 means that today, much of the remaining glasswork 297 00:22:15,120 --> 00:22:17,800 is covered in a layer of toxic lead powder. 298 00:22:19,360 --> 00:22:23,520 It was really painful to see the catastrophe on TV. 299 00:22:23,520 --> 00:22:27,200 I was looking to see what's up and around the windows. 300 00:22:28,440 --> 00:22:30,160 And it was, of course, 301 00:22:30,160 --> 00:22:33,440 totally difficult to have a good idea of what's happened. 302 00:22:33,440 --> 00:22:38,280 There is a before and after 15th April for historical monuments, 303 00:22:38,280 --> 00:22:39,520 that's for sure. 304 00:22:40,680 --> 00:22:45,760 Glass scientist Claudine Loisel uses a hand-held digital microscope 305 00:22:45,760 --> 00:22:49,480 to investigate the levels of lead powder on the stained glass. 306 00:22:49,480 --> 00:22:53,760 She must then formulate a strategy to clean every single panel. 307 00:22:53,760 --> 00:22:56,520 It's a vast decontamination programme 308 00:22:56,520 --> 00:23:00,160 that will make the glass safe for restorers to begin work. 309 00:23:03,120 --> 00:23:07,120 This window is in the back of the cathedral in the lower level, 310 00:23:07,120 --> 00:23:09,200 furthest from the inferno, 311 00:23:09,200 --> 00:23:12,520 but it's still badly contaminated. 312 00:23:12,520 --> 00:23:15,120 CLAUDINE SPEAKS IN FRENCH 313 00:23:15,120 --> 00:23:19,000 Fortunately, these windows have not been cleaned for 100 years, 314 00:23:19,000 --> 00:23:22,000 so the lead has settled on top of a dust layer, 315 00:23:22,000 --> 00:23:23,640 not on the glass itself. 316 00:23:25,080 --> 00:23:29,720 The first thick layer of deposit was, we can say, 317 00:23:29,720 --> 00:23:32,120 as a small protection in one way. 318 00:23:32,120 --> 00:23:36,000 So, we have just to remove all the deposit to clean 319 00:23:36,000 --> 00:23:38,480 these windows from the 19th century. 320 00:23:38,480 --> 00:23:42,120 Claudine examines deposits from windows around the cathedral. 321 00:23:42,120 --> 00:23:44,080 The samples reveal vital clues 322 00:23:44,080 --> 00:23:46,960 about the spread of the lead contamination. 323 00:23:46,960 --> 00:23:52,080 After the spire fell, the cloud of dust, lead and different particle 324 00:23:52,080 --> 00:23:54,400 pushed in the other direction. 325 00:23:54,400 --> 00:23:57,520 So, we are a little bit more protected in this area. 326 00:23:57,520 --> 00:24:00,560 The windows of the upper level in the path of the lead cloud 327 00:24:00,560 --> 00:24:02,320 have been most contaminated. 328 00:24:05,080 --> 00:24:07,880 The team takes out and transports these panels 329 00:24:07,880 --> 00:24:09,800 to this special laboratory, 330 00:24:09,800 --> 00:24:13,080 where they experiment with ways to remove the lead. 331 00:24:15,920 --> 00:24:19,480 First, Claudine uses a precision vacuum cleaner 332 00:24:19,480 --> 00:24:22,080 to hoover up the 100 years of dust 333 00:24:22,080 --> 00:24:25,600 and most of the lead powder along with it. 334 00:24:25,600 --> 00:24:31,720 So, this is a good way to protect the conservator. 335 00:24:31,720 --> 00:24:34,040 You can control the action, 336 00:24:34,040 --> 00:24:38,760 the pressure on the glass and also on the painting. 337 00:24:38,760 --> 00:24:41,720 Then she uses water and cotton balls 338 00:24:41,720 --> 00:24:45,080 to meticulously remove the last of the lead. 339 00:24:45,080 --> 00:24:49,720 Of course, you need scientific evidence that it's working. 340 00:24:49,720 --> 00:24:54,360 Claudine uses X-ray spectroscopy to measure exactly how many wipes 341 00:24:54,360 --> 00:24:57,240 it takes to bring the lead down to normal levels. 342 00:24:57,240 --> 00:25:04,240 So, we can identify each chemical element we have in the material. 343 00:25:04,240 --> 00:25:07,080 Too few wipes and the lead will remain. 344 00:25:07,080 --> 00:25:10,920 Too many wipes and restoration will take longer than necessary. 345 00:25:13,400 --> 00:25:17,560 OK, now, this analyses if it's finished. 346 00:25:17,560 --> 00:25:21,120 After five wipes with the distilled water, 347 00:25:21,120 --> 00:25:24,240 Claudine checks to see if the glass is decontaminated. 348 00:25:26,960 --> 00:25:30,080 OK, we have different chemical elements, 349 00:25:30,080 --> 00:25:32,480 calcium, iron. 350 00:25:32,480 --> 00:25:36,680 And if we want to see the lead, there is no lead. 351 00:25:36,680 --> 00:25:38,720 CLAUDINE LAUGHS 352 00:25:38,720 --> 00:25:42,120 After nine months, we can see a good solution, 353 00:25:42,120 --> 00:25:44,080 a good way to clean and to preserve 354 00:25:44,080 --> 00:25:46,840 the stained glass windows from Notre-Dame. 355 00:25:51,960 --> 00:25:55,560 The upper-level windows were not only in the path of the lead cloud, 356 00:25:55,560 --> 00:25:57,920 but also closest to the inferno. 357 00:26:00,520 --> 00:26:04,960 Claudine hunts for hairline cracks caused by thermal shock, 358 00:26:04,960 --> 00:26:08,120 the rapid heating and cooling of the glass. 359 00:26:08,120 --> 00:26:10,920 This is one window from the choir 360 00:26:10,920 --> 00:26:14,640 and we have two panels from the middle of the...bay. 361 00:26:15,640 --> 00:26:17,240 But here we have a crack. 362 00:26:19,120 --> 00:26:21,360 The hand-held digital microscope 363 00:26:21,360 --> 00:26:24,000 helps Claudine see deep into the crack. 364 00:26:24,000 --> 00:26:27,880 If it's caused by the fire, it will be clean and fresh. 365 00:26:27,880 --> 00:26:31,400 If it's older, it will be full of residue. 366 00:26:31,400 --> 00:26:35,440 We can see the well-defined line of the crack. 367 00:26:35,440 --> 00:26:38,160 We have no residue, 368 00:26:38,160 --> 00:26:43,240 so, we can say this crack is due to the fire. 369 00:26:43,240 --> 00:26:47,160 This is a recent crack and this is typical thermal shock. 370 00:26:47,160 --> 00:26:50,000 It looks like the upper-level stained glass 371 00:26:50,000 --> 00:26:52,760 will need to be painstakingly glued back together. 372 00:26:54,800 --> 00:26:58,000 But inside Notre-Dame, the lower-level stained glass 373 00:26:58,000 --> 00:27:01,160 appears to have survived unscathed. 374 00:27:01,160 --> 00:27:05,880 And, yeah, we can see we have a good stability 375 00:27:05,880 --> 00:27:09,120 around of the painting. 376 00:27:09,120 --> 00:27:11,560 So, there is absolutely no thermal shock. 377 00:27:11,560 --> 00:27:14,440 So, that's good news for us. 378 00:27:17,520 --> 00:27:22,080 On site, the teams of scientists meet the engineers and architects 379 00:27:22,080 --> 00:27:23,840 to share their findings. 380 00:27:23,840 --> 00:27:26,760 CLAUDINE SPEAKS IN FRENCH 381 00:27:31,880 --> 00:27:34,760 Once Claudine's team has restored Notre-Dame's glasswork 382 00:27:34,760 --> 00:27:36,400 to its former glory, 383 00:27:36,400 --> 00:27:40,000 they may use a radical new preservation technique 384 00:27:40,000 --> 00:27:42,400 to safeguard it for future generations. 385 00:27:45,400 --> 00:27:49,320 It's being used on a huge scale here in northern England. 386 00:27:51,320 --> 00:27:53,920 This is York Minster, 387 00:27:53,920 --> 00:27:56,520 an 800-year-old Gothic masterpiece 388 00:27:56,520 --> 00:28:01,480 and home to the largest expanse of medieval stained glass in the UK, 389 00:28:01,480 --> 00:28:03,360 the Great East Window. 390 00:28:04,960 --> 00:28:07,880 It is one of the largest windows ever made anywhere 391 00:28:07,880 --> 00:28:09,440 in the medieval world. 392 00:28:09,440 --> 00:28:13,840 We've got glass from the 12th right through to the 18th century 393 00:28:13,840 --> 00:28:16,160 in quite significant quantities. 394 00:28:16,160 --> 00:28:20,200 And it is really our national treasure house of stained glass. 395 00:28:23,240 --> 00:28:27,280 Engineers here are completing a £10 million project 396 00:28:27,280 --> 00:28:31,760 to protect York Minster's stained glass from harmful UV rays 397 00:28:31,760 --> 00:28:34,160 and the corrosive effects of moisture. 398 00:28:34,160 --> 00:28:36,360 In modern stained glass conservation, 399 00:28:36,360 --> 00:28:38,720 we're really doing as much as we can 400 00:28:38,720 --> 00:28:43,680 to keep both surfaces of the historic stained glass dry and stable, 401 00:28:43,680 --> 00:28:46,160 and that's where our ventilated 402 00:28:46,160 --> 00:28:49,440 environmental protective glazing comes into play. 403 00:28:52,080 --> 00:28:54,000 Right, I can see that I'm almost in. 404 00:28:57,760 --> 00:28:59,840 I think it's just this last bit, here. 405 00:28:59,840 --> 00:29:03,520 Matt Nickels is installing this new conservation system. 406 00:29:03,520 --> 00:29:08,040 He slots a protective clear glass exterior frame 407 00:29:08,040 --> 00:29:09,640 into the window opening. 408 00:29:09,640 --> 00:29:12,920 And this goes into the original glazing groove 409 00:29:12,920 --> 00:29:15,120 where the medieval glass would have been. 410 00:29:15,120 --> 00:29:20,200 This protective glazing prevents corrosive condensation from forming 411 00:29:20,200 --> 00:29:23,840 on the 800-year-old stained glass that will sit behind it. 412 00:29:23,840 --> 00:29:27,960 The gap created means that there's air circulation running through, 413 00:29:27,960 --> 00:29:32,160 and when you've got air circulation, it's regulating the temperature, 414 00:29:32,160 --> 00:29:35,200 which means that there's less moisture on the glass. 415 00:29:35,200 --> 00:29:39,800 Each frame is custom-made and takes great skill to fit. 416 00:29:41,000 --> 00:29:42,800 You don't want to make it too small 417 00:29:42,800 --> 00:29:45,040 because it's going to obviously slide through. 418 00:29:45,040 --> 00:29:47,600 No two windows are going to be the same. 419 00:29:47,600 --> 00:29:50,080 With the outer panel installed, 420 00:29:50,080 --> 00:29:53,920 they can reinstate the layer of medieval glass. 421 00:29:53,920 --> 00:29:56,080 They're actually in fairly good condition 422 00:29:56,080 --> 00:29:59,520 considering that they're early 13th century. 423 00:29:59,520 --> 00:30:02,920 There's always the worry whenever you're handling glass like this, 424 00:30:02,920 --> 00:30:06,480 but you've just got to make sure that you're really, really careful. 425 00:30:08,440 --> 00:30:12,000 There's nothing quite like seeing it with sunlight behind it. 426 00:30:12,000 --> 00:30:14,840 When you put it up like this, it's quite magical, isn't it? 427 00:30:17,800 --> 00:30:22,040 Techniques like this offer a glimpse of how scientists like Claudine 428 00:30:22,040 --> 00:30:25,600 may eventually preserve Notre-Dame's glass. 429 00:30:25,600 --> 00:30:29,960 This is the best way to protect a stained glass window. 430 00:30:29,960 --> 00:30:31,880 So, it will be, for sure, 431 00:30:31,880 --> 00:30:34,640 an option to protect the windows from Notre-Dame. 432 00:30:37,720 --> 00:30:39,960 By an incredible stroke of luck, 433 00:30:39,960 --> 00:30:43,400 the three spectacular rose windows of Notre-Dame, 434 00:30:43,400 --> 00:30:45,640 that date from the 13th century, 435 00:30:45,640 --> 00:30:47,840 survived the fire intact. 436 00:30:47,840 --> 00:30:53,320 It was a great relief to see all the panel in place, 437 00:30:53,320 --> 00:30:54,760 in good stability. 438 00:30:54,760 --> 00:30:58,400 So, it was really, "Phew, everything is OK." 439 00:30:58,400 --> 00:31:00,960 Had the vaulting collapsed next to the windows, 440 00:31:00,960 --> 00:31:03,960 the glass could have been badly damaged. 441 00:31:03,960 --> 00:31:05,760 But luckily, the stone vaulting, 442 00:31:05,760 --> 00:31:08,840 which sits just under the timber and lead roof, 443 00:31:08,840 --> 00:31:11,800 protected the windows from the inferno above. 444 00:31:32,120 --> 00:31:35,200 The magnificent vaulting was built to be resilient, 445 00:31:35,200 --> 00:31:38,720 thanks to precise medieval craftsmanship 446 00:31:38,720 --> 00:31:42,400 using an estimated 800 cubic metres of limestone. 447 00:31:46,040 --> 00:31:48,760 The arches work together to support the roof 448 00:31:48,760 --> 00:31:50,440 and stabilise the outer walls. 449 00:31:53,720 --> 00:31:58,280 But the intense heat from the fire and the collapsing spire... 450 00:31:59,960 --> 00:32:02,560 ..took out 15% of the stone vaulting. 451 00:32:04,160 --> 00:32:08,560 Today, three 12-metre-wide holes and several smaller gaps 452 00:32:08,560 --> 00:32:10,920 mean the vaults could collapse at any moment. 453 00:32:14,400 --> 00:32:18,000 The team collects, stores and catalogues the fallen stone 454 00:32:18,000 --> 00:32:21,040 in this tent located alongside the cathedral. 455 00:32:22,920 --> 00:32:25,000 They may be able to use some of this stone 456 00:32:25,000 --> 00:32:26,440 to reconstruct the vaults. 457 00:32:31,640 --> 00:32:35,080 But medieval masons never intended the stone to be subject 458 00:32:35,080 --> 00:32:39,360 to an 800-degree inferno, then soaked with tonnes of water. 459 00:32:40,960 --> 00:32:43,200 Now, without a roof to protect it, 460 00:32:43,200 --> 00:32:46,200 areas of the vaulting are exposed to the elements. 461 00:32:47,200 --> 00:32:50,000 Stone scientist Jean-Didier Mertz 462 00:32:50,000 --> 00:32:54,400 forces mercury at high pressure through samples of the damaged vaulting 463 00:32:54,400 --> 00:32:57,040 to calculate the porosity of the stones. 464 00:32:58,360 --> 00:33:01,360 This tells him how sponge-like the stonework has become 465 00:33:01,360 --> 00:33:03,200 one year on from the fire. 466 00:33:03,200 --> 00:33:07,200 The damage produced some cracks due to the fire. 467 00:33:07,200 --> 00:33:10,840 With these cracks, it is possible to the water 468 00:33:10,840 --> 00:33:13,480 to go in and to fill all the cracks. 469 00:33:14,680 --> 00:33:17,560 Jean-Didier confirms the surface of the vaulting stones 470 00:33:17,560 --> 00:33:19,640 are covered with micro cracks, 471 00:33:19,640 --> 00:33:22,120 dramatically increasing the porosity. 472 00:33:26,560 --> 00:33:29,120 Greater porosity means the vaulting can absorb more water 473 00:33:29,120 --> 00:33:33,320 than they thought, potentially swelling the blocks. 474 00:33:33,320 --> 00:33:35,760 As the blocks dry, they then shrink. 475 00:33:37,480 --> 00:33:40,760 Jean-Didier has dried this vaulting stone under lab conditions. 476 00:33:42,120 --> 00:33:45,280 He knows the block holds two kilos of water 477 00:33:45,280 --> 00:33:48,400 and takes six months to fully dry. 478 00:33:48,400 --> 00:33:51,880 The vault of Notre-Dame, it is not exactly the same 479 00:33:51,880 --> 00:33:56,400 because the cathedral is not completely sealed. 480 00:33:56,400 --> 00:34:02,200 And with new rainwater 481 00:34:02,200 --> 00:34:05,240 and the repeated cycle of swelling and shrinkage, 482 00:34:05,240 --> 00:34:07,640 it is a real decay... 483 00:34:08,960 --> 00:34:11,360 ..the weathering of the material. 484 00:34:11,360 --> 00:34:15,160 Even if some fallen vaulting stone can be reused, 485 00:34:15,160 --> 00:34:18,200 it's clear they'll also need to source new stone. 486 00:34:31,080 --> 00:34:34,720 Notre-Dame is made up of many different types of limestone. 487 00:34:36,040 --> 00:34:39,040 Medieval masons chose hard limestone for the towers, 488 00:34:39,040 --> 00:34:43,320 pillars and outer walls to build tall and hold up the roof. 489 00:34:46,520 --> 00:34:50,440 For the sculptures, they chose dense, fine-grained limestone 490 00:34:50,440 --> 00:34:53,120 that can be carved with great detail. 491 00:34:53,120 --> 00:34:57,640 And for the vaults, they selected softer, more porous limestone 492 00:34:57,640 --> 00:34:59,280 that's light, but strong. 493 00:35:01,560 --> 00:35:06,040 If the team rebuilding the vaults picks a limestone that is too heavy, 494 00:35:06,040 --> 00:35:09,240 the new vaults may not last as long as they should. 495 00:35:11,880 --> 00:35:16,600 Geologist Lise Leroux investigates what quarry this stone came from. 496 00:35:16,600 --> 00:35:23,280 We have some blocks coming from the collapse of the vault for study. 497 00:35:23,280 --> 00:35:27,520 This detective work will help the team source replacement stone 498 00:35:27,520 --> 00:35:30,720 that shares identical mechanical properties. 499 00:35:30,720 --> 00:35:32,440 We have to verify... 500 00:35:32,440 --> 00:35:36,200 The fallen vaulting stone contains a rare microfossil 501 00:35:36,200 --> 00:35:40,880 called Orbitolites complanatus, a kind of plankton. 502 00:35:40,880 --> 00:35:45,440 Fossils like this are found in just one layer of rock. 503 00:35:45,440 --> 00:35:50,480 This will make sourcing new stone of the same type even trickier. 504 00:35:50,480 --> 00:35:53,200 Can they use this geological fingerprint 505 00:35:53,200 --> 00:35:56,400 to discover the original source of the vaulting stone? 506 00:36:00,200 --> 00:36:04,760 To find out, Lise and fellow Notre-Dame scientist Claudine Loisel 507 00:36:04,760 --> 00:36:07,960 venture deep beneath Paris. 508 00:36:09,800 --> 00:36:14,080 Hidden under the city streets is a rich source of limestone, 509 00:36:14,080 --> 00:36:17,680 a vast labyrinth of quarry tunnels. 510 00:36:17,680 --> 00:36:23,600 Lise and Claudine enter this maze, two miles south of Notre-Dame 511 00:36:23,600 --> 00:36:25,440 in the famous Catacombs. 512 00:36:26,880 --> 00:36:28,280 Ah! 513 00:36:28,280 --> 00:36:30,160 Ah, oui! 514 00:36:49,720 --> 00:36:51,440 In the late 18th century, 515 00:36:51,440 --> 00:36:54,840 the quarries were given a different purpose 516 00:36:54,840 --> 00:36:59,000 and they housed bones from old cemeteries... 517 00:37:00,720 --> 00:37:02,960 ..which were inside the towns, 518 00:37:02,960 --> 00:37:06,720 cemeteries which were closed at the end of the 18th century 519 00:37:06,720 --> 00:37:07,960 for sanitary reasons. 520 00:37:09,360 --> 00:37:11,920 Amongst the bones, Lise and Claudine 521 00:37:11,920 --> 00:37:14,560 find traces left by the medieval miners. 522 00:37:36,320 --> 00:37:37,640 D'accord. 523 00:37:43,040 --> 00:37:44,280 Mm. 524 00:37:47,440 --> 00:37:50,560 The upper level of the quarry holds hard limestone 525 00:37:50,560 --> 00:37:53,720 with large, well-preserved fossils. 526 00:37:53,720 --> 00:37:59,760 These fossils are more characteristic of limestones 527 00:37:59,760 --> 00:38:02,120 used for the pillars, 528 00:38:02,120 --> 00:38:04,280 the arch in Notre-Dame. 529 00:38:04,280 --> 00:38:05,640 But not for the vaults. 530 00:38:06,840 --> 00:38:10,600 Lise and Claudine hope to find a match for the soft vaulting stone 531 00:38:10,600 --> 00:38:12,200 in the lower level of the quarry. 532 00:38:14,120 --> 00:38:21,040 We now...to look if we can find the specific microfossils. 533 00:38:24,480 --> 00:38:29,680 I'm not sure because on the surface it's very rough 534 00:38:29,680 --> 00:38:34,640 and it's not so clear because of the state of the surface. 535 00:38:34,640 --> 00:38:36,960 The limestone here is softer, 536 00:38:36,960 --> 00:38:40,520 but Lise cannot see a match for the rare microfossil 537 00:38:40,520 --> 00:38:43,240 found in the Notre-Dame vaulting sample. 538 00:38:47,280 --> 00:38:50,960 So, back in the lab, she takes a closer look at a sample 539 00:38:50,960 --> 00:38:53,360 of limestone from the lower level of the quarry. 540 00:38:55,640 --> 00:38:57,560 These little fossils... 541 00:38:58,640 --> 00:39:01,760 ..this one, this one, this one 542 00:39:01,760 --> 00:39:05,600 are, in fact, some planktonic fossils 543 00:39:05,600 --> 00:39:08,920 which are called foraminifera. 544 00:39:08,920 --> 00:39:12,840 It's not the fossil signature she's looking for. 545 00:39:12,840 --> 00:39:14,040 But then... 546 00:39:15,920 --> 00:39:17,160 Oh! 547 00:39:19,120 --> 00:39:23,880 This one here is Orbitolites complanatus. 548 00:39:23,880 --> 00:39:30,000 This little planktonic fossil is a dating fossil, 549 00:39:30,000 --> 00:39:35,760 which match with the stone coming from the vault. 550 00:39:35,760 --> 00:39:38,640 It's a stratigraphic indicator, 551 00:39:38,640 --> 00:39:42,480 characteristic from the middle Oligocene, 552 00:39:42,480 --> 00:39:46,120 which is a geological age of deposit. 553 00:39:47,480 --> 00:39:50,600 Lise confirms the origin of the Notre-Dame vaulting stone. 554 00:39:51,720 --> 00:39:55,880 It's quarried from the deepest seams of limestone beneath Paris. 555 00:39:55,880 --> 00:39:57,120 Conclusive. 556 00:39:57,120 --> 00:40:01,400 But what about the harder limestone used by medieval masons to build 557 00:40:01,400 --> 00:40:04,640 Notre-Dame's load-bearing pillars and arches? 558 00:40:04,640 --> 00:40:07,080 Another microfossil signature 559 00:40:07,080 --> 00:40:09,840 confirms the origin of this type as well. 560 00:40:09,840 --> 00:40:13,360 The arches are built with a hard stone, 561 00:40:13,360 --> 00:40:17,400 with a resistant stone to support the vault. 562 00:40:17,400 --> 00:40:21,320 And the vault in itself is logically constructed 563 00:40:21,320 --> 00:40:25,080 with a lighter, more porous stone. 564 00:40:25,080 --> 00:40:28,840 And in the quarry located in Paris, 565 00:40:28,840 --> 00:40:31,720 we have these two kinds of stone. 566 00:40:31,720 --> 00:40:36,120 Medieval masons knew exactly how to exploit the varying mechanical 567 00:40:36,120 --> 00:40:38,960 properties of the limestone for Notre-Dame, 568 00:40:38,960 --> 00:40:42,360 knowledge passed down through the generations. 569 00:40:42,360 --> 00:40:46,840 Sourcing more of the correct stone won't be easy. 570 00:40:46,840 --> 00:40:49,440 The old quarries are no longer active, 571 00:40:49,440 --> 00:40:53,000 but engineers now know what limestone to look for. 572 00:40:53,000 --> 00:40:57,320 This will help them find a match in quarries outside Paris. 573 00:41:01,160 --> 00:41:05,320 Stone is not the only raw material that will need to be replaced 574 00:41:05,320 --> 00:41:07,280 as engineers reconstruct Notre-Dame. 575 00:41:08,800 --> 00:41:11,880 The timber roof was also a medieval wonder. 576 00:41:15,520 --> 00:41:19,240 It was constructed from 700 cubic metres of timber, 577 00:41:19,240 --> 00:41:21,600 cut from 52 acres of oak. 578 00:41:21,600 --> 00:41:24,640 That's approximately 1,300 trees. 579 00:41:28,840 --> 00:41:31,960 For this reason, it was known as the "Forest". 580 00:41:31,960 --> 00:41:35,600 Every single oak in Notre-Dame's Forest was hand-picked 581 00:41:35,600 --> 00:41:39,080 for the physical properties needed in the roof structure, 582 00:41:39,080 --> 00:41:42,120 from dense straight oak for pillars, 583 00:41:42,120 --> 00:41:44,600 to curved oak for support arches. 584 00:41:51,800 --> 00:41:54,920 But the fire consumed every beam in the Forest. 585 00:41:56,760 --> 00:42:03,040 Today, this intricate 500-tonne timber jigsaw lies in ruins. 586 00:42:03,040 --> 00:42:04,880 SPEAKS IN FRENCH 587 00:42:21,440 --> 00:42:26,160 Over 50 tonnes of the precious roof timber lie precariously on top of the vaults. 588 00:42:27,200 --> 00:42:29,440 Despite the destruction, 589 00:42:29,440 --> 00:42:32,800 every single beam holds the history of Notre-Dame. 590 00:42:32,800 --> 00:42:35,160 It has deep archaeological value. 591 00:42:36,640 --> 00:42:39,520 It's vital that workers forensically record the position 592 00:42:39,520 --> 00:42:42,680 where each beam fell before they remove them. 593 00:42:43,720 --> 00:42:46,520 This helps them determine where it originally sat 594 00:42:46,520 --> 00:42:48,160 in the roof structure. 595 00:42:49,320 --> 00:42:52,040 These highly trained rope access technicians 596 00:42:52,040 --> 00:42:55,200 catalogue and clear the charred timber on the vaults. 597 00:42:57,840 --> 00:43:00,160 THEY SPEAK IN FRENCH 598 00:43:01,840 --> 00:43:04,120 It's not possible to walk on the vaults, 599 00:43:04,120 --> 00:43:06,560 because the structure is very precarious. 600 00:43:06,560 --> 00:43:10,120 They needed to create a way to access with ropes. 601 00:43:12,680 --> 00:43:14,960 We need to wear a special mask 602 00:43:14,960 --> 00:43:18,200 because of the lead dust that we might inhale. 603 00:43:22,400 --> 00:43:26,640 We label the timbers and we mark them with a code 604 00:43:26,640 --> 00:43:30,040 that the architects will be able to identify. 605 00:43:35,480 --> 00:43:37,560 The team has their work cut out. 606 00:43:37,560 --> 00:43:41,080 There are thousands of separate pieces of timber to catalogue. 607 00:43:41,080 --> 00:43:43,280 We have a lot of work to do. 608 00:43:43,280 --> 00:43:45,640 That's why we're working day and night. 609 00:43:45,640 --> 00:43:49,080 They've already extracted around 4,000 pieces. 610 00:43:55,320 --> 00:44:00,320 Timber scientist Catherine Lavier begins painstaking detective work 611 00:44:00,320 --> 00:44:04,800 to reveal how Notre-Dame's vast Forest was originally assembled 612 00:44:04,800 --> 00:44:07,200 and could be rebuilt today. 613 00:44:09,200 --> 00:44:12,240 Some pieces were very well preserved 614 00:44:12,240 --> 00:44:16,520 because, as you see here, with different faces 615 00:44:16,520 --> 00:44:21,160 and another piece of wood is coming here with a wooden joint here 616 00:44:21,160 --> 00:44:23,160 to assemble them. 617 00:44:23,160 --> 00:44:26,400 And it's rather typical from the medieval period. 618 00:44:27,800 --> 00:44:30,960 And here you have a mark... 619 00:44:33,360 --> 00:44:35,280 ..of carpenters. 620 00:44:35,280 --> 00:44:38,840 So, they are sure that this piece with this piece are together. 621 00:44:40,280 --> 00:44:42,560 It's very important for carpenters. 622 00:44:42,560 --> 00:44:44,920 They prepare the wood on the ground. 623 00:44:44,920 --> 00:44:49,200 And after that, they go to the roof and reassemble again. 624 00:44:50,640 --> 00:44:53,880 Every carpenter has his own way to mark. 625 00:44:53,880 --> 00:44:59,040 But in general, it's based on the Roman numbers. 626 00:44:59,040 --> 00:45:03,760 But we can find some differences between teams of carpenters. 627 00:45:05,680 --> 00:45:09,000 We were very surprised to find that, because I thought everything 628 00:45:09,000 --> 00:45:10,320 will be destroyed. 629 00:45:10,320 --> 00:45:12,200 And finally not. 630 00:45:12,200 --> 00:45:15,800 The tree rings of the timbers conceal further clues. 631 00:45:15,800 --> 00:45:19,000 Each ring represents one year of growth, 632 00:45:19,000 --> 00:45:23,840 a time capsule of information about the life of the tree in that year. 633 00:45:23,840 --> 00:45:28,480 Catherine analyses core samples from Notre-Dame's roof trusses. 634 00:45:30,280 --> 00:45:33,600 She measures each ring to reveal the secret story 635 00:45:33,600 --> 00:45:37,280 of the very oak trees the structure was made from. 636 00:45:37,280 --> 00:45:39,360 SHE SPEAKS IN FRENCH 637 00:46:08,400 --> 00:46:10,640 Catherine is gaining new insight 638 00:46:10,640 --> 00:46:13,120 into the types of trees best suited 639 00:46:13,120 --> 00:46:16,760 to rebuild the complex Forest of Notre-Dame. 640 00:46:16,760 --> 00:46:21,360 This extraordinary challenge will require around 1,300 oak trees... 641 00:46:22,760 --> 00:46:27,520 ..craftspeople versed in the lost art of medieval carpentry practices 642 00:46:27,520 --> 00:46:32,800 and a blueprint for possibly the most complex timber structure in Europe. 643 00:46:34,440 --> 00:46:37,400 The one person who may possess the key to unlock 644 00:46:37,400 --> 00:46:42,320 the lost Forest's geometrical secrets is architect Remi Fromont. 645 00:46:43,360 --> 00:46:48,840 In 2014, Remi spent the entire year mapping every inch of the timber. 646 00:47:02,320 --> 00:47:04,640 We are collecting photographs... 647 00:47:12,720 --> 00:47:16,040 The fire at Notre-Dame triggers a race across France 648 00:47:16,040 --> 00:47:20,240 to 3D-scan historical monuments inside and out. 649 00:47:22,000 --> 00:47:26,640 These represent a digital insurance policy to preserve French heritage. 650 00:47:30,440 --> 00:47:33,560 The laser bounces off each contour in the room. 651 00:47:33,560 --> 00:47:38,440 The machine then measures the time it takes for the laser to return. 652 00:47:38,440 --> 00:47:43,360 Millions of measurements form a cloud of data called a point cloud. 653 00:47:45,640 --> 00:47:49,520 In 2016, researchers used this same technology 654 00:47:49,520 --> 00:47:52,960 to create a full point cloud of Notre-Dame's 655 00:47:52,960 --> 00:47:55,000 lost timber roof structure. 656 00:47:55,000 --> 00:48:00,440 This remarkable 3D scan will combine with Remi's 2014 survey 657 00:48:00,440 --> 00:48:03,720 in Livio's digital twin for Notre-Dame. 658 00:48:03,720 --> 00:48:08,960 What we are producing today will be probably the information 659 00:48:08,960 --> 00:48:11,120 usable for the next generations. 660 00:48:11,120 --> 00:48:15,160 The team now has the data they need to rebuild the timber roof 661 00:48:15,160 --> 00:48:17,640 with the exact same geometry. 662 00:48:17,640 --> 00:48:20,240 And the 500 tonnes of new oak needed 663 00:48:20,240 --> 00:48:22,920 could come from forests like this. 664 00:48:25,120 --> 00:48:28,360 Almost a third of France is covered with forest. 665 00:48:28,360 --> 00:48:30,800 Oak was a vital strategic resource 666 00:48:30,800 --> 00:48:33,320 throughout the Middle Ages and the Renaissance. 667 00:48:35,680 --> 00:48:39,760 Vast forests were needed to build cities and expand navies. 668 00:48:42,400 --> 00:48:45,400 Felling and carving oak for Notre-Dame's roof 669 00:48:45,400 --> 00:48:49,920 requires carpenters skilled in using medieval tools and techniques 670 00:48:49,920 --> 00:48:53,560 like this team who keep the old ways alive to this day. 671 00:48:53,560 --> 00:48:56,960 We rebuild buildings using only hand tools 672 00:48:56,960 --> 00:48:58,600 and no power tools at all. 673 00:49:00,120 --> 00:49:04,400 Using this kind of tool, you don't apply your vision on the tree. 674 00:49:04,400 --> 00:49:09,600 You...you have your work influenced by the shape of the tree itself. 675 00:49:09,600 --> 00:49:15,280 Today, carpenter Leo Rousseau has the honour of felling his first tree 676 00:49:15,280 --> 00:49:17,200 using techniques from the Middle Ages. 677 00:49:18,960 --> 00:49:23,840 Ah, yeah, it's like everything, it takes practice. 678 00:49:23,840 --> 00:49:27,480 You don't have to go to the sports room at night. 679 00:49:28,920 --> 00:49:31,480 You don't want your tree to fall into another trees, 680 00:49:31,480 --> 00:49:35,120 because you want to use the other trees for the next generations. 681 00:49:35,120 --> 00:49:39,280 So, the idea is to create here a hinge that gives you 682 00:49:39,280 --> 00:49:41,920 the direction where you want the tree to fall. 683 00:49:41,920 --> 00:49:44,640 And then you cut from the back for the tree to fall. 684 00:49:50,960 --> 00:49:52,880 THEY SPEAK IN FRENCH 685 00:50:01,240 --> 00:50:06,800 Leo now has a taste of what it took for the Notre-Dame carpenters 686 00:50:06,800 --> 00:50:10,200 to source the 1,300 oaks for the roof timbers. 687 00:50:14,240 --> 00:50:18,960 I like the feeling that you have to put so much effort into one tree. 688 00:50:18,960 --> 00:50:21,600 It gives you a little bit of respect 689 00:50:21,600 --> 00:50:25,840 on what you're going to do with that particular beam or... 690 00:50:25,840 --> 00:50:28,160 Yeah, it's a different feeling. 691 00:50:29,960 --> 00:50:32,000 Carpenters are using the old ways to restore 692 00:50:32,000 --> 00:50:35,160 the Chateau de Beaumesnil in Normandy. 693 00:50:35,160 --> 00:50:37,360 It's a national historic monument 694 00:50:37,360 --> 00:50:40,920 built on the site of an 1,100-year-old castle. 695 00:50:40,920 --> 00:50:43,360 SPEAKS IN FRENCH 696 00:50:48,560 --> 00:50:50,960 The chateau has seen better days. 697 00:50:50,960 --> 00:50:54,520 The curved beams that hold up the roof are close to collapse 698 00:50:54,520 --> 00:50:56,040 and must be replaced. 699 00:50:58,760 --> 00:51:01,280 SHE SPEAKS IN FRENCH 700 00:51:15,920 --> 00:51:19,480 The carpenters here face many of the same challenges 701 00:51:19,480 --> 00:51:22,680 that Notre-Dame restorers will need to overcome 702 00:51:22,680 --> 00:51:25,880 when they rebuild the cathedral's lost Forest. 703 00:51:27,320 --> 00:51:29,080 The timber has been chosen 704 00:51:29,080 --> 00:51:33,440 so the curve of the grain perfectly matches the curve of the new beam. 705 00:51:33,440 --> 00:51:37,920 If you get a straight tree which has a straight grain 706 00:51:37,920 --> 00:51:44,080 and then you get a curved piece of wood inside of this... 707 00:51:45,440 --> 00:51:49,080 So, here is the fibre so it can break right there. 708 00:51:49,080 --> 00:51:52,920 But if you take the tree that's curved, 709 00:51:52,920 --> 00:51:57,400 the fibre is like this, so it cannot break. 710 00:51:57,400 --> 00:52:01,560 You keep all of the structural strength of the...of the tree. 711 00:52:05,640 --> 00:52:08,280 They use an original beam to produce a template 712 00:52:08,280 --> 00:52:10,600 and mark out the new beam on the oak. 713 00:52:13,000 --> 00:52:17,000 The carpenters who built Notre-Dame would be familiar with the tools 714 00:52:17,000 --> 00:52:20,120 this team uses to hew the raw timber. 715 00:52:23,400 --> 00:52:25,960 So, we would start with these axes. 716 00:52:27,880 --> 00:52:31,640 You know, it's a long handle, which gives you a long swing. 717 00:52:33,200 --> 00:52:38,240 Because if you want to make notches cutting deep in the wood, 718 00:52:38,240 --> 00:52:43,720 so you want a long handle to give you momentum and use the weight 719 00:52:43,720 --> 00:52:46,760 of the tool itself to basically do the job. 720 00:52:48,600 --> 00:52:51,600 And after you've split most of the wood, 721 00:52:51,600 --> 00:52:56,080 you use a second type of axe, which is called a broad axe. 722 00:52:56,080 --> 00:52:59,920 They have a single bevel, long cutting edge 723 00:52:59,920 --> 00:53:03,440 and the handle is offset. 724 00:53:04,680 --> 00:53:09,040 So, if you're working as you go down, 725 00:53:09,040 --> 00:53:13,720 your hand here, you see I'm not hitting the...this sharp edge. 726 00:53:16,320 --> 00:53:21,000 For skilled carpenters, cutting Notre-Dame's roof timbers with axes 727 00:53:21,000 --> 00:53:24,880 compared to a modern sawmill would take roughly twice the time. 728 00:53:26,800 --> 00:53:29,200 This curved oak will be one of ten 729 00:53:29,200 --> 00:53:33,640 the team needs to install as part of the chateau roof restoration. 730 00:53:33,640 --> 00:53:38,080 It sits alongside this 400-year-old original beam. 731 00:53:38,080 --> 00:53:40,200 HE SPEAKS IN FRENCH 732 00:53:52,720 --> 00:53:56,600 Just like the Notre-Dame beams, the chateau's original beam 733 00:53:56,600 --> 00:53:59,800 holds messages from the old carpenters. 734 00:54:09,400 --> 00:54:11,800 French carpenters have the oak, 735 00:54:11,800 --> 00:54:13,520 they have the skills 736 00:54:13,520 --> 00:54:16,760 and they have the plans required to reconstruct 737 00:54:16,760 --> 00:54:19,800 Notre-Dame's vast Forest of roof timbers. 738 00:54:27,200 --> 00:54:30,960 While the architects consider options for rebuilding the roof, 739 00:54:30,960 --> 00:54:34,320 they must also work out what innovations to engineer 740 00:54:34,320 --> 00:54:38,040 into the structure to safeguard it against future fires. 741 00:54:40,520 --> 00:54:44,840 Scientists here at the University of Edinburgh School of Engineering 742 00:54:44,840 --> 00:54:47,000 use scale models to investigate 743 00:54:47,000 --> 00:54:49,760 how fires spread through timber structures 744 00:54:49,760 --> 00:54:52,120 like the Forest of Notre-Dame. 745 00:54:52,120 --> 00:54:55,120 Our job is to understand the underlying physics 746 00:54:55,120 --> 00:54:58,800 and then to use our understanding of the physics to create strategies 747 00:54:58,800 --> 00:55:00,720 by which people can be more safe 748 00:55:00,720 --> 00:55:02,840 and assets can be more safe from fire. 749 00:55:04,120 --> 00:55:06,120 As Luke ignites a single beam 750 00:55:06,120 --> 00:55:08,920 in this model of a timber roof structure... 751 00:55:08,920 --> 00:55:10,680 Ignition. 752 00:55:10,680 --> 00:55:14,400 ..it becomes clear how quickly the energy radiates 753 00:55:14,400 --> 00:55:19,000 to the timber beam alongside until it too catches fire. 754 00:55:20,360 --> 00:55:23,320 This phenomenon is called reradiation. 755 00:55:23,320 --> 00:55:25,640 In a structure like a roof at Notre-Dame, 756 00:55:25,640 --> 00:55:29,120 what we had is a collection of timber members in a nice pattern, 757 00:55:29,120 --> 00:55:31,760 all kind of looking at each other as they burn. 758 00:55:31,760 --> 00:55:33,840 And that fact that they're looking at each other, 759 00:55:33,840 --> 00:55:35,360 they're radiating at each other, 760 00:55:35,360 --> 00:55:37,400 is what causes the fire to grow and escalate 761 00:55:37,400 --> 00:55:39,200 in such a dramatic way. 762 00:55:39,200 --> 00:55:40,800 If you create a gap or a firebreak 763 00:55:40,800 --> 00:55:42,880 within your network of timber elements, 764 00:55:42,880 --> 00:55:45,720 you can prevent the combustion from occurring 765 00:55:45,720 --> 00:55:48,120 on the far side of the firebreak. 766 00:55:49,600 --> 00:55:51,840 To stop the spread of fires like this, 767 00:55:51,840 --> 00:55:55,560 today, engineers build fire-separating partitions 768 00:55:55,560 --> 00:55:57,520 into the roofs of historic buildings. 769 00:56:01,200 --> 00:56:05,880 These firewalls are erected inside the roof of York Minster. 770 00:56:05,880 --> 00:56:07,480 In the event of a fire, 771 00:56:07,480 --> 00:56:11,520 they should prevent the reradiation and transfer of energy. 772 00:56:11,520 --> 00:56:16,560 Innovations like this could help safeguard Notre-Dame's new roof 773 00:56:16,560 --> 00:56:18,440 against future threats. 774 00:56:25,360 --> 00:56:29,840 One year after the fire that ravaged Notre-Dame Cathedral, 775 00:56:29,840 --> 00:56:34,280 investigators have still not pinpointed the cause of the blaze. 776 00:56:34,280 --> 00:56:38,760 And immense challenges and uncertainties still lie ahead. 777 00:56:38,760 --> 00:56:41,800 The building is not yet out of danger. 778 00:56:41,800 --> 00:56:46,680 Over the next 12 months, engineers must remove the melted scaffolding 779 00:56:46,680 --> 00:56:50,360 and seal the cathedral roof to make it watertight. 780 00:56:50,360 --> 00:56:52,760 Then they can stabilise the weakened vaulting. 781 00:56:53,960 --> 00:56:58,640 It's a monumental feat, and rebuilding the entire cathedral 782 00:56:58,640 --> 00:57:02,920 could take much longer than the five years decreed by President Macron. 783 00:57:21,000 --> 00:57:24,960 Architects around the world have unleashed their imagination 784 00:57:24,960 --> 00:57:28,920 to submit grand plans for what the new spire above Notre-Dame 785 00:57:28,920 --> 00:57:30,600 could look like... 786 00:57:30,600 --> 00:57:33,840 ..from mirrored roofs with kaleidoscopic pinnacles 787 00:57:33,840 --> 00:57:37,600 and vast solar panels powering nearby buildings, 788 00:57:37,600 --> 00:57:42,520 to stained glass edifices that will light up the Paris skyline. 789 00:57:44,320 --> 00:57:46,560 However Notre-Dame is rebuilt, 790 00:57:46,560 --> 00:57:49,680 the unique collaboration of architects and scientists 791 00:57:49,680 --> 00:57:53,240 is rewriting how we understand the very fabric 792 00:57:53,240 --> 00:57:55,520 of this magnificent cathedral. 793 00:57:55,520 --> 00:57:59,240 I think the fire in some ways helped remind a lot of people 794 00:57:59,240 --> 00:58:01,800 what an important part of our sort of shared history 795 00:58:01,800 --> 00:58:03,440 and shared culture this is. 796 00:58:03,440 --> 00:58:07,520 Soon, a complete digital twin of Notre-Dame 797 00:58:07,520 --> 00:58:11,960 should allow future generations of craftspeople to maintain, 798 00:58:11,960 --> 00:58:15,640 protect and faithfully rebuild Notre-Dame... 799 00:58:16,840 --> 00:58:18,960 ..as many times as necessary. 67476

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