In Asterix The Gaul, there is a Roman soldier who runs off to fetch a superior, and his name is mentioned as Caius Marchéopus. What is the exact pun being performed here?
Marché aux puces.
The phrase is similar in both languages, "flea" being a puce in French. I doubt the two phrases originated separately and Wikipedia suggests it was used first in French. The phrase is the same in many other European languages (Italian, German, Danish, Portuguese…) and it states also it comes from the French marché aux puces.
It comes from the town of Saint-Ouen, at the door of Paris. Many peoples were selling old clothes and old varied objects there to the poors of Paris. They didn't have the right to do it in Paris intra muros.
Today, the Saint-Ouen's flea market is known across the world for antiquities.