It’s a beautiful (if chilly) day to visit Les Arenes de Lutece, the oldest monument in the city. Built in the first century AD, this amphitheatre could seat some 17,000 for plays, circuses, and the odd gladiator games. Note the animal cages! The arena is usually pretty sparsely peopled; this morning there’s wasn’t much more than a couple of kids on metal scooters and an art class.
As with so many sites dating back this far, this one was covered over and forgotten for hundreds of years. It had turned into a cemetery at one point, and had a convent on it at another. The 20th century rediscovery happened when the city was starting to turn it into a depot for public transportation.