The twin medieval towers of one of the most famous landmarks in Paris were saved, but its 300-foot spire collapsed and two-thirds of its roof was destroyed. The fire also endangered its vast collection of Christian relics and artwork.

The details: The cause of the fire remains unknown. Notre-Dame had been undergoing restoration work, which fire experts said can result in open flames or sparks from equipment. Here’s what we know and don’t know.

Closer look: We have photographs of the cathedral through the ages and video of the disaster. Using images and maps, we also traced how the fire spread.

Another angle: As France struggles to cope with recent social and political unrest, the symbolism of the blaze was hard to miss, our architecture critic writes.