To the east of the Colle della Villetta lie the ruins of a large Roman building, known in the 19th C. as the Torraccia or San Cesareo Rotunda. It is a large nymphaeum with a central plan on two floors. Originally it was square on the exterior and round on the interior. The upper storey on the other hand was octagonal.
In the lower part, at the four corners, there were circular exedras, overtopped by large windows in the upper part. The vault was decorated with octagonal lacunars, while the wall decoration was provided by a polychrome facing in precious marbles.
From available evidence we know that originally the structure measured 20.5 metres in diameter internally and was 18 m. high.
From the building technique used and the kind of structure it is, the monument can be dated to around the beginning of the 4th C., at a time where the Roman Emperor Maxentius used to live here.

Galleria fotografica