From the New York Times:
In just over an hour, a fire spread through the wooden attic of the Notre-Dame Cathedral in Paris and toppled its 300-foot spire on Monday.
Around 6:30 p.m., Paris time, smoke began to pour out of the cathedral’s roof, near scaffolding that had been put up over the last few months to conduct renovations on the spire.
The fire started in the cathedral’s attic, said Jean-Claude Gallet, commander of the Paris firefighters.
The attic is an oddly shaped space, seldom visited, that lies above the soaring stone arches visible from the floor of old European cathedrals. Diagrams of Notre-Dame and official descriptions of the space indicate that it is crisscrossed by giant, timber trusses that add structural integrity to the cathedral.