The Maritime Theater is absolutely unique, the symbolic building of Villa Adriana together with the Canopus.

It is an artificial island surrounded by a circular canal which had the same function as the moat in medieval castles: it allowed complete isolation from the rest of the Villa and was the emperor's private "buen retiro".

In ancient times it was accessed via two small wooden swing bridges that rotated on special tracks; currently there is a masonry bridge, but the island is closed to the public.
The canal is surrounded by a circular portico with Ionic capitals, where some doors connected it with the Hall of the Philosophers and the Greek Library.

As often happens with the buildings of Hadrian's Villa, the name is imaginary, and has changed over the centuries. In the sixteenth century Pirro Ligorio called it 'La Rota’ (the Wheel), due to its round shape; then it became the 'Natatorio' because you could swim in its circular canal.

At the end of the nineteenth century, the French architect Blondel invented the name Maritime Theatre, probably due to the beautiful friezes with animals and sea monsters that once decorated it.

They are an example of the extraordinary imagination and creativity of the sculptors that decorated Villa Adriana. They show fantastic and monstrous creatures, with the heads and wings of animals or the body of a Triton or a Cupid, and all ending in a fish's tail. They swim on a sea of ​​barely visible waves.
In one fragment we see a griffin and a goat, or a panther facing a goat. In others ones there is a Triton between a lioness and a lion, a dolphin or a dragon ridden by a cupid.

The friezes were removed together with the columns and other precious marbles and are today found in various museums. Some are in the Antiquarium of the Villa, others in the Accademia dei Lincei in Rome, or in the Villa d'Este in Tivoli.
Some were brought by Cardinal Farnese to the Horti Farnesiani in Rome, still others have been traced to Percile not far from Rome, in the church of Santa Maria della Vittoria: Finally three fragments were walled up as decoration in the complex of Villa Doria Pamphili. The Doria Pamphiljs purchased several ancient marbles in Tivoli in 1645-46.

These friezes are unique and were «custom made» for the emperor only. They decorated the architraves of the curved colonnades of the island, and in fact some are concave and others convex.