Colosseum

The Colosseum, or the Coliseum, is an elliptical amphitheatre in the centre of the city of Rome, Italy, the largest ever built in the Roman Empire, built of concrete and stone. It is considered one of the greatest works of Roman architecture and Roman engineering.

The Mark of Athena
The twin giants Otis and Ephialtes are battled there by Percy Jackson and Jason Grace, and defeated by the god Bacchus.