Dating to the 1st century BC, this great drum of a mausoleum encloses a burial chamber, now roofless. In the 14th century it was converted into a fort by the Caetani family, who were related to Pope Boniface VIII, and used to frighten passing traffic into paying a toll.
The tomb was built for the daughter of the consul Quintus Metellus Creticus. Cecilia Metella was of particular significance as she joined two important families by marriage – she was also daughter-in-law of Crassus, Julius Caesar's banker. The walls are made of travertine and the interior is decorated with a sculpted frieze featuring Gaelic shields, ox skulls and festoons.