Rocca dei Papi, Medieval fortress in Montefiascone, Italy.

Rocca dei Papi is a medieval fortress in Montefiascone, a hilltop town sitting above Lake Bolsena in the Viterbo province of Lazio. The structure is made of thick stone walls and several towers that rise above the surrounding countryside.

The fortress was built in the early 13th century on the orders of Pope Innocent III to control the trade routes passing through the area. Pope Urban V later used it as a summer residence during the second half of the 14th century.

The museum on the ground floor, opened in 2006, is named after Antonio da Sangallo the Younger, who worked on modernising the fortress in the early 16th century. It holds photographs and sketches illustrating his work. On the pillars supporting the arcades are two inscriptions bearing the date 1516 and the name of Pope Leo X, marking the completion of works he commissioned.

The site sits on a hill, so sturdy footwear and a reasonable level of fitness are helpful before heading up. From the upper parts of the fortress, the view stretches over Lake Bolsena and the surrounding hills.

The transparent floor slabs in the palace reveal Lombard-era tombs (6th–7th century) found during the 1980s restorations. The small museum on the ground floor, open since 2006, is dedicated to Antonio da Sangallo the Younger and holds photographs and sketches of his work, not original drawings.