An outdoor arena offers evidence of Roman France, or Gaul as it used to be known. The Roman City was called Lutetia. The old main Roman road is not Rue Saint-Jacques.
There's no charge to walk about this area preserved in a residential neighborhood. A little imagination reminds us of times when people watched others engage in deadly combat. Now it's a play area and worth a quick look (Arènes de Lutèce ). It was rediscovered in 1860 by Victor Hugo.
In addition, there's a crypt by Notre Dame, which contains a view of Roman Baths and artifacts. This find is fairly recent (1960s) and was opened in 1980. And it dates to some 2,000 years ago.
To find the crypt, go to the front of Notre Dame de Paris cathedral. Here's a link to the website http://www.crypte.paris.fr/en/crypt.
Note: As of early 2020, the crypt is closed to the public because of the cathedral fire. I did not see an indication of when it would re-open.
