PARIS — By the time the Paris Fire Department’s chaplain made his way inside Notre-Dame, flames had already consumed most of the cathedral’s roof and its spire had smashed onto the nave.

But the flames had yet to reach many of the artworks, artifacts and relics, and it was the Rev. Jean-Marc Fournier’s job to guide his colleagues through the many chapels and alleys of the burning cathedral and tell them which to save first.

“I had two priorities: to save the crown of thorns and the Blessed Sacrament,” Father Fournier said, referring to the consecrated bread and wine of the Eucharist.