Archaeological Crypt in Notre-Dame

In past trips, we've been inside Notre Dame, but never inside the Archaeological Crypt under the cathedral.  We decided to do the audio tour and we were glad we did.  It was very interesting and informative.  In the crypt, there are ruins of the city of Paris, before and during Roman times.  We learned about the origins of the city. Paris was originally only on the larger island and the Seine River protected the city like a natural moat.  Obviously the city expanded to first the left bank and then the right bank.