Pope Gregory X (Latin: Gregorius X; ca. 1210 – 10 January 1276), born Teobaldo Visconti, was Pope from 1 September 1271 to his death in 1276. 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.
Gregory succeeded Pope Clement IV in 1271 after the papal chair had been vacant for three years due to divisions among the Cardinals. The College of Cardinals was equally split between French and Italian Cardinals who wanted a Pope from their country due to the ongoing political situation with Charles of Anjou, younger brother of King Louis IX of France, who had usurped the throne of Sicily by arms and perpetually intervened in the political affairs of the entire Italian peninsula. The deadlock was finally broken when the citizens of Viterbo, where the Cardinals were assembled, removed the roof from the building they were meeting in and locked them in, only allowing them bread and water. More than a year later, the Cardinals elected Pope Gregory X. He was considered a strong choice because even though he was Italian, he had spent most of his career north of the Alps and thus had not been embroiled in recent Italian political controversies.
Gregory's election came as a complete surprise to him, partially because it happened while he was engaged in the Ninth Crusade at Acre with King Edward I of England in Palestine. Not wanting to leave his mission, his first action as Pope was to send out appeals for aid to the Crusaders, and at his final sermon at Acre just before leaving to sail for Italy, he famously remarked, "If I forget thee, O Jerusalem, let my right hand forget her cunning" (a quote from Psalm 137).
Sometime during his reign as Pope, Gregory wrote a letter against the charges of "blood libel" and persecution against the Jews.
Writing in L’Osservatore Romano, Agostino Paravicini Bagliani says that the popular belief that St. Pius V (1566-72) was the first Pope to wear the white cassock is inaccurate. Instead, writes Bagliani, the first document that mentions the Pope’s white cassock dates from 1274. “The first pope to be solemnly invested with the red mantle immediately after his election was Gregory VII,” the scholar added, noting that traditionally “from the moment of his election the Pope put on vestments of two colors: red (cope, mozzetta, shoes); and white (cassock, socks).”
As soon as he was elected in 1271, Pope Gregory received a letter from the MongolGreat KhanKublai, remitted by Niccolo and Matteo Polo following their travels to his court in Mongolia. Kublai was asking for the dispatch of a hundred missionaries, and some oil from the lamp of the Holy Sepulcher. The new Pope could spare only two friars and some lamp oil. The friars turned back soon after the party left for Mongolia. The two Polos (this time accompanied by the young Marco Polo, who was then 17 years old) returned to the Mongol Empire and remitted the oil from the Pope to Kublai in 1275.
The Mongol Ilkhanate leader Abaqa sent a delegation with over a dozen members to the 1274 Council of Lyon, where plans were made for possible military cooperation between the Mongols and the Europeans. After the Council, Abaqa sent another embassy led by the Georgian Vassali brothers to further notify Western leaders of military preparations. Gregory answered that his legates would accompany the Crusade, and that they would be in charge of coordinating military operations with the Il-Khan. However, these projects for a major new Crusade essentially came to a halt with the death of Gregory X on 10 January 1276. The money which had been saved to finance the expedition was instead distributed in Italy.