- [Narrator] The church has survived all kinds of disasters, from floods to political violence.
(stone shattering) - Cathedrals are built as a kind of triumph over adversity.
- [Narrator] After 60 years, as they near what they believe is the end of construction, the builders realize their work of art has a significant flaw that might endanger its future.
(speaking in foreign language) - [Translator] There were no gutters, no system for collecting rainwater.
- [Translator] Water has always been the great enemy of architects.
- [Narrator] Water running down the exterior walls of the cathedral seeps into and erodes the stone and causes cracks when frozen.
For a building the size of Notre-Dame, the problem of water removal is on an extreme scale.
An average downpour means nearly 7,000 gallons of water must be drained away.
(speaking in foreign language) - [translator]} Notre-Dame's Architects had the brilliant idea of using the tops of the flying buttresses as gutters.
- [Narrator] As the flying buttresses are hollowed out, they are then connected, forming large network for water collection.
Throughout the system, water shoots out of the gargoyle statues' mouths, away from the church walls.
This effective drainage system, restored by Viollet-le-Duc and maintained since, is still at work today.
(impressive orchestral music) (thunder rumbling) Engineering this water removal system in the Middle Ages brings spectacular changes to the cathedral.
The builders dismantle the roof and raise the church walls by six and a half feet.
They transform the small terrace roofs and rework the flying buttresses.
The structure supporting the roof is entirely remounted: 1,2000 tons of wood and lead.
And the builders take the opportunity to crown Notre-Dame with a spire.
During this new phase, the windows are expanded and extended, a technical exploit that puts the building far ahead of other cathedrals under construction.
- This is one very obvious way in which the builders of Notre-Dame modernized during the process.
- They kept changing their minds.
They had no sense that they were working in an old tradition; they were working at the cutting edge of technology.