Pope Gregory X (c.1210 - 10 January 1276), born Teobaldo Visconti, was Pope from 1 September 1271 to his death in 1276 and was a member of the Secular Franciscan Order. He was elected at the conclusion of a papal election that ran from 1268 to 1271, the longest papal election in the history of the Catholic Church. The first cathedral of Arezzo was built on the nearby Pionta Hill, over the burial place of Donatus of Arezzo, martyred in 363. In 1203 Pope Innocent III had the cathedral moved within the city's walls, to the current site. The construction of the current structure, started in 1278, went through different phases, and ended in 1511. The facade was built in 1901-1914, replacing the previous, unfinished one, dating to the 15th century.