Voltaire isn’t buried in Paris, exactly.
Or at least not in a place where you’d want to go visit his gravesite. Voltaire, real name: Francois-Marie Arouet, made a lot of enemies in his life because of his brilliant satires and treatises, especially those that attacked the intolerance, corruption, and irrationality of the religious establishment.
When he died in 1778 and could no longer defend himself, those enemies struck back. He was denied burial in church ground until the abbey in Champagne relented. In 1791, his remains were moved to a place of honor within the Pantheon in Paris.
However, in 1814 a group of right-wing religious extremists decided that burial was too good for someone who had so hurt their feelings in his lifetime, so they broke in one night, stole Voltaire’s remains, and dumped them in a garbage heap somewhere.
Their craven act wasn’t discovered for more than fifty years, so while the memorial in the Pantheon remains, his sarcophagus is but an empty shell.
Before his burial, his heart and brain had been removed. While his brain disappeared after being auctioned off in the late 1800s, his heart is still in France’s possession—last time they checked at least—in the Bibliotheque Nationale, hopefully under a decent lock and key.