Jean-Claude Gallet, the commander, had a backup plan: Colossus, a 1,100-pound tanklike robot with the ability to venture into danger zones where conditions would quickly kill a person.

Using a motorized water cannon capable of firing more than 660 gallons per minute, Colossus took aim at the stone walls of the ancient cathedral and began spraying. In an interview with the Times of London, Gallet credited the firefighting robot with lowering temperatures inside the glass-filled nave and saving the lives of its human counterparts as an even greater disaster loomed.

“Time was against us, the wind was against us and we had to get the upper hand,” Gabriel Plus, a spokesman for the fire brigade, told the paper. “The priority we set was to save the two belfries. Imagine if the timber of the belfries had been weakened and the bells had collapsed. That was really our fear. In the beginning, it was not impossible to imagine that the cathedral structure could collapse.”