Palazzo dei Papi is a palace in Viterbo, northern Latium, Italy. It is one of the most important monuments in the city, situated alongside the Duomo di Viterbo. The Papal Curia was removed to Viterbo in 1257 by Alexander IV, due to the hostility of the Roman commune and constant urban violence: the former bishop's palace of Viterbo was enlarged to provide the Popes with an adequate residence. The construction, commissioned by the Capitano del popolo Raniero Gatti, provided a great audience hall communicating with a loggia raised on a barrel vault above the city street. It was completed probably around 1266.
The massive façade, facing the central piazza San Lorenzo which is dominated by the Duomo, is approached by a wide staircase completed in 1267. The top of the palace walls is decorated with square merlons. On the right is a wide roofless loggia with a seven-bay arcade, supported by slender doubled columns and decorated with crests and reliefs. Within the loggia is a 15th-century fountain, made with material of various ages, sporting the coat of arms of the Gatti family.
Viterbo remained the papal seat for twenty-four years, from 1257 to 1281.