A papal conclave is a gathering of the College of Cardinals convened to elect a bishop of Rome, also known as the pope. Catholics consider the pope to be the apostolic successor of Saint Peter and the earthly head of the Catholic Church. Concerns around political interference led to reforms after the interregnum of 1268–1271 and Pope Gregory X's decree during the Second Council of Lyons in 1274 that the cardinal electors should be locked in seclusion (Latin for 'with a key') and not permitted to leave until a new pope had been elected. Conclaves are now held in the Sistine Chapel of the Apostolic Palace in Vatican City. Since the Apostolic Age, the bishop of Rome, like other bishops, was chosen by the consensus of the clergy and laity of the diocese. The body of electors was more precisely defined when, in 1059, the College of Cardinals was designated the sole body of electors. Since then, other details of the process have developed. In 1970, Pope Paul VI limited the electors to cardinals under 80 years of age in Ingravescentem aetatem. The procedures were established by Pope John Paul II in his apostolic constitution, Universi Dominici gregis, as amended by Pope Benedict XVI in 2007 and 2013. A two-thirds supermajority vote is required to elect the new pope. The last papal conclave occurred in 2013, when Jorge Mario Bergoglio was elected as Pope Francis, succeeding Benedict XVI. Historical development The procedures for the election of the pope developed over almost two millennia. Until the College of Cardinals was created in 1059, the bishops of Rome, like those in other areas, were elected by acclamation of the local clergy and people. Procedures similar to the present system were introduced in 1274 when Gregory X promulgated Ubi periculum following the action of the magistrates of Viterbo during the interregnum of 1268–1271. The process was further refined by Gregory XV with his 1621 bull Aeterni Patris Filius, which established the requirement of a two-thirds majority of cardinal electors to elect a pope. The Third Lateran Council had initially set the requirement that two-thirds of the cardinals were needed to elect a pope in 1179. This requirement has varied since then, depending on whether the winning candidate was allowed to vote for himself, in which cases the required majority was two-thirds plus one vote. Aeterni Patris Filius prohibited this practice and established two-thirds