The Rocca dei Papi stands on the highest point of the Montefiascone hill. The period of greatest prestige for the structure was the Middle Ages, when Pope Innocent III chose it as the seat of province of the Papal States. It became a particularly important institutional political center: during Avignon captivity (1303 -1377) it welcomed legates sent by Avignon. Many Popes and important catholic character influenced "Rocca" like Pope Urban V or Cesare Borgia. At the end of the XV century he gave commision to Antonio da Sangallo the Elder carried out a project to restructure the fortress, in order to adapt the architectural complex to the new war requirements arising from the use of firearms.
Under the pontificate of Giulio II della Rovere the architect Antonio da Sangallo the Younger worked, who carried out the last interventions for the palace, which ended in 1516. Currently the structure is composed of a courtyard, in which archaeological remains are visible: the base of the watchtower, dating back to the 11th-12th century, phase of the first fortification; some medieval and Renaissance walls; a double-barreled cistern, built during the renovation of the castle, carried out on the commission of Popes Urban IV and Martin IV in the second half of the thirteenth century.
Under the portico, designed by Antonio da Sangallo the Younger, some burials of the early Middle Ages can be seen and there is the entrance to the Museum of Architecture by Antonio da Sangallo the Younger. From the corner tower of the fortress, called Torre del Pellegrino, you can enjoy a splendid view of Lake Bolsena and the surrounding countryside.