Arènes de Lutèce

     The Arènes de Lutèces are the remains of a Gallo-Roman amphitheater which was built in the first century A.D.  It is located in the Latin Quarter, an area on the left bank of the Seine River, in the fifth and sixth arrondissements.  This arena could hold 15,000 people.  The amphitheater was sacked by barbarians in 280 A.D.  Later some of the stones were carted off to be used in other building projects.  Around 1210, the arena was filled in.  It was discovered in 1883 and restored by 1918.
http://en.wikipedia.org/wiki/Ar%C3%A8nes_de_Lut%C3%A8ce

The entrance.

People kick soccer balls around or play games of pétanque (aka boules or bocce ball).

The ancient wall as seen from the street.  The arena is located at 47 rue Monge.

The passage to the inside.

An arched entry.

One side is shared with modern buildings.