The Flavian Amphitheatre in Rome — the Colosseum — is the largest amphitheatre of the ancient world and a manifesto of Rome's real architectural contribution: the systematic use of the arch and the vault. Where the Greek temple rests on post-and-lintel, Rome roofs space with the arch.

The building is organised radially on an elliptical plan: walls running outward from the centre and the ring corridors around them, carrying barrel vaults, form a structural grid. This grid both supports the tiers of seating (cavea) and manages the flow of the crowd. The materials are cleverly graded: hard travertine in the foundations and main piers, tufa and brick in the intermediate walls, light Roman concrete in the upper vaults. Heavy loads go to durable stone below, light roofing to concrete above.

The circulation solution remains modern even today: numbered entrances directed spectators to the sector on their ticket; vaulted exit mouths called "vomitoria" let an estimated crowd of 50,000 empty in minutes. Above, a fabric awning (velarium) strung from great masts provided shade. The Colosseum thus unites arch-and-vault structure, material hierarchy, and mass circulation in a single multi-storey typology — the ancestor of every later stadium.