A pope is chosen by the College of Cardinals meeting in a papal conclave, a process refined over nine centuries. Early bishops of Rome were elected by the clergy and people of the city, a pattern vulnerable to interference by Roman factions and, later, by emperors and kings. The Second Lateran Council of 1139 and especially the 1179 decree of the Third Lateran Council placed election firmly in the hands of the cardinals, requiring a two-thirds majority. The word conclave, from the Latin for with a key, dates to 1268 to 1271, when the citizens of Viterbo locked the cardinals in and reduced their rations to force a decision after nearly three years of deadlock, a crisis that produced the sealed, sequestered election procedure still used today.
Only cardinal-electors under the age of eighty may vote, gathering in the Sistine Chapel until a candidate secures two-thirds support; ballots are burned after each round, with chemical additives producing black smoke for an inconclusive vote and white smoke to announce a new pope. Any baptized Catholic man is technically eligible, but every pope since 1378 has been chosen from among the cardinals themselves.
Notable holders include Gregory the Great, who reorganized the Church's finances and mission to England around 600; Leo the Great, who met with Attila the Hun in 452; Urban II, who launched the First Crusade in 1095; and John Paul II, whose twenty-seven-year papacy was the third-longest recorded and included a central role in the collapse of European communism. Benedict XVI's 2013 resignation was the first in six centuries and set a modern precedent for a living pope emeritus.