This monument was built under the emperor Augustus in honour of Cecilia Metella, the  daughter of a Roman consul. It is a round mausoleum raised on a square base, similar to that of Augustus himself, only smaller. In 1303 it  was incorporated in the Castrum Caetani and became the main tower of that fortification. The castle, built over the solidified lava flows called Capo di Bove (from a volcano eruption that took place  300 000 years ago) still shows its medieval characteristics and is witness to the power of the family of Pope Boniface VIII. It is now possible to visit the underground levels. The tomb and the castle, together, offer an interesting example of the construction techniques and materials used from antiquity to the middle ages.