Conversation

The fire warning system at Notre-Dame took dozens of experts six years to put together, and in the end involved thousands of pages of diagrams, maps, spreadsheets and contracts, according to archival documents found in a suburban Paris library by The Times.

The result was a system so arcane that when it was called upon to do the one thing that mattered — warn “fire!” and say where — it produced instead a nearly indecipherable message.

It made a calamity almost inevitable, fire experts consulted by The Times said.