Pope Gregory X [SEP] date of death
Pope Gregory X
Pope Gregory X (;  – 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.
He convened the Second Council of Lyon and also made new regulations in regards to papal conclaves. Though briefly annulled by Pope Adrian V and Pope John XXI,
of the Apostolic throne, Adrian V appointed Cardinal Bertrand de Saint-Martin and two other cardinals to go to King Charles I of Sicily, who was in Rome, and invite him to come to Viterbo to swear his feudal oath of allegiance to the pope.
The third Conclave of 1276, should have begun in Viterbo ten days after the death of Pope Adrian, according to the Constitution of Gregory X, "Ubi Periculum". The date should have been 28 August or 29 August. But Pope Adrian had suspended