Fundamental fire prevention safeguards — like firewalls or a sprinkler system — were absent by choice, so as not to alter the cathedral’s design or heighten risk by introducing electrical wiring to “the forest,” as the fragile attic of the building is known.

Early estimates place the reconstruction effort at between five and 15 years, and more than $600 million has already been pledged.

What we know: The cathedral’s twin medieval towers survived, but its 300-foot spire collapsed, and two-thirds of its roof was destroyed. No one was killed, but one firefighter and two police officers were injured.

The treasures: The fire endangered Notre-Dame’s vast collection of Christian artworks and relics. Some significant items have suffered, but many were saved, including a relic of what many believe is the crown of thorns worn by Jesus.

And by some miracle of timing, the copper sculptures on the spire also escaped a fiery end — they were removed for restoration just days before the blaze.