What is the oldest building in Paris?

Answer 1

Well, it's hard to answer your question. If you are talking about the oldest house in Paris, the answer above is correct.

But there are Roman ruin in Paris dating from the 1st century AD, such as the Thermes de Cluny (the Roman baths) or the Arènes de Lutèce (amphitheatre). So those are probably the oldest buildings since they are about 2000 years old.

The oldest church in Paris is Eglise St-Germain des Prés (6th to 12th centuries). It achieved its final form as we know it now at the time the construction of Notre Dame cathedral began (1163).

The oldest (still existing) bridge is the Pont Neuf (1578-1607).

Answer 2

51 rue Montmorency, reportedly built in 1407. Originally a homeless shelter and soup kitchen, it was at some point owned by the alchemist Nicolas Flamel and now houses a tavern named after him.

Another possibility is 3 rue Volta, although there is no official record of its construction date.