This is an ancient Roman amphitheater and is one of the oldest and best preserved of this kind.
It was built around 70 BC and was used for circus games and fights between gladiators, as also confirmed by numerous graffiti that advertised such events.
It’s “cavea” where the seats were placed, was divided into three zones: the ima cavea, where the personalities of the city would sit, the media cavea, that’s to say the central area reserved to common people and the summa cavea, the higher orders for women.
To protect the spectators from sun or rain, the amphitheater was designed to use the "velarium" ie an awning, usually in linen, which was stretched to cover the entire area of the structure.