The Roman Amphitheatre dating from AD 90 had a capacity of 20,000 spectators in its heyday. Remarkably well preserved, it saw service as a stone quarry during the later Middle Ages after serving as a fortress. Later on it became a small fortified town with watchtowers, three of which remain, complete with houses and churches!
Gladiators fought and died here as no doubt did thousands of Christians and others. However, in 404 AD the enlightened Emperor Honorious banned this type of activity. Nevertheless, Les Arènes as it is called by the French, carries on this tradition of public spectacle still, being the home of the twice yearly Feria which is the Provençal version of the Spanish bullfight.
If you wish to visit this and other monuments consider buying a Pass Monuments Liberté for all the monuments of Arles.