Notre Dame started off as a center for paganism.
Construction on the cathedral began in 1163, though it didn't wrap up until long after; while the towers were completed in 1245.
It was first home to a Pagan temple, which Romans built after Julius Caesar led them to occupy the city in 52 BC.
We know that Maurice de Sully, Bishop in 1160 wanted to reconstruct the site where Norte Dame is today. That same site is where a Roman church and Pagan temple once existed.
The Île-de-la-Cité on which Notre-Dame de Paris now stands was once a Pagan Gallo-Roman city known as Lutetia.
The cathedral may have been built right over it.
You may be hearing lots of people mention that Notre Dame was a Pagan temple before and are maybe wondering about this, whether it's true, and why it was like that.
Since it's one of my favorite historical subjects, I'll explain what I know.
Most churches in Europe older than 600 years were built on former Pagan sites. This was actually official church "policy." Popes (especially Gregory "the great") specifically ordered that new churches be built on old Pagan sites. In some cases, wood and stone from the old sites (temples, groves, etc) would be used partially in the church.
The idea was that it would be easier to convert people to the new religion if it seemed like the new places were merely continuations of the old.
They didn't come up with idea, though. It's what the Roman Empire did, too. They often re-carved old statues and standing stones with new images to fit their imperial religion, also changing the names of local gods to make them Roman. This is a lot like what the Catholic Church did with saints, many of whom had Pagan roots or were pagan gods.
So most of the oldest churches in Europe actually have two (or more) layers of Pagan sites below them: one Roman pagan on top of an "indigenous" (or pre-Roman) one.
The best know example of this is in Paris: Notre Dame, which was a temple to Jupiter during Roman conquest and a smaller shrine (suspected of being a goddess shrine) before the Romans conquered and built their own temple.
Incidentally, there's another church with two much older Pagan sites below it, except it was only consecrated one hundred years ago (1919). That church is the basilica of the sacred heart (Sacré Couer) on Montmartre, and is dedicated to "expiate the sins" of the Paris Commune.
The hill it's on, Montmartre (the red-light district where the Moulin Rouge is), was once a Roman site dedicated to Dionysos and Mars, and before that it was a Druid mount.
So even though the last official Pagan worship on the place ended more than a thousand years ago, people are *still* building Churches on Pagan sites.
From a Pagan perspective, this makes complete sense (even if we'd rather see the old temples and groves back). Because places don't stop being sacred just because the buildings on them are destroyed. It isn't the humans who make it holy, it's the spirits of the place and the land itself.
Sacred sites are places you can communicate with gods easiest, "wells of power" or "crossroads" or "places where the veil is thin" or however else you want to describe it.
So whatever the dominant religion, even if it's a "secular" one, it makes sense for the religious buildings to be in those places and not elsewhere. And even if the people choosing the site aren't aware of the theory behind it (but the Catholic Church is a lot more magically-adept than most people give them credit for), they unconsciously sense this truth.
So anyway, Notre Dame is burning. But the place was sacred before, and the building isn't what made it sacred. So mourn the loss of art and the destruction of a symbol, but don't mourn the loss of the sacred: it's not going anywhere.
