The Eglise Saint-Séverin is in the Latin Quarter of Paris, not far from the Sorbonne and Notre-Dame. The current church building dates back to the first half of the 13th century, but an earlier church on the site was already "in business" in the late 11th. It's a church in the Gothic style but with, as usual, subsequent modifications.
The building in the foreground, along the sidewalk, is the old charnel house. It dates from the Middle Ages, when the custom was, when the cemetery ran out of space, to remove the the bones from the graves and store them in this structure. It's the only charnel house that still exists in Paris, according to the Michelin guide.
When I took these pictures of the back end of the church, I was walking down the Rue Saint-Jacques toward the Seine and Notre-Dame. La rue Saint-Jacques is one of the oldest streets in Paris. It was the Roman road leading south from Lutèce (Roman Paris) and may well pre-date the Roman conquest of Gaul.