Days after fire raced through the attic of the beloved Notre-Dame cathedral in Paris, experts cautioned that stabilization of the structure and rebuilding true to a heritage that stretches back to the 12th century would not be quick nor easy.

The French government, which owns and maintains Notre-Dame, was well aware of the fire risk of the heavy-timber structure that supported the roof—so dense with beams and braces that it was referred to as “the forest.” The government had wired the building with detectors and had full-time fire inspectors on site. After the first alarm on the evening of April 15, a marshal failed to locate the fire, causing a critical delay. By the time firefighters reached the flames, it had become a conflagration.