The office of the pope (Bishop of Rome), derives its name from the Greek papas and Latin papa, which are familiar forms of ‘father’. In early times many bishops and even priests were called popes, but in the Western Church the word gradually became a title restricted to the Bishop of Rome; Pope Gregory VII in 1073 forbade its use for anyone except the Bishop of Rome. The traditional enumeration lists 266 holders of the office, excluding antipopes, beginning with St Peter and reaching to the present holder Benedict XVI. The basis of papal authority derives from St Peter's position of leadership among the 12 Apostles, given him by Jesus Christ, the early tradition that he came to Rome and was martyred there. The papal claim to extend its jurisdiction over all Christian Churches was a major cause of various Churches breaking with Rome, notably the Orthodox Church definitively in 1054, and the Protestant Churches at the time of the Reformation in the 16th century.