What is the circular arena the Romans played sports in called?

The Colosseum is/was a large circular arena.

The Roman arenas were the amphitheatres. They were not necessarily circular. They were often oval. They hosted gladiatorial combats, venationes (animal slaying), chariot contests and executions. They differed from theatres which were semicircular, circuses which were very long (they hosted horse races with and without chariots) and the stadia used for athletics.Around 230 amphitheatres have been found