The Mauseleo dei Plauzi stands near the Ponte Lucano in Tivoli. It was originally built in the 12th century by Emperor Barbarossa for his family. Later it also served for a time as a defense tower.
Mausoleo dei Plauzi Tivoli
Useful information

Address: Via Lago di Vico – 00010 – Tivoli. The monument is completely dilapidated and can be visited free of charge.
History and description
The Mausoleum dei Plauzi (or Plautii) was built by Plauzio Silvano, to whom it also owes its name.
It was constructed in 1155, when Emperor Barbarossa met with Pope Adrian IV. The pope gave the emperor the keys to the city, after which the latter decided to have a mausoleum built for his family near the Ponte Lucano.
In the Middle Ages, the monument was converted into a defense tower.
Changes were also made to the exterior in 1465.
Ponte Lucano
The bridge itself consists of five arches, though not all of them are visible anymore.