"Catholicos" means "the general head", and can be considered equivalent to "universal bishop." The early church had three priestly ranks: "episcopos" (bishop), priest and deacon. By the end of the third century, bishops of important cities in the Roman Empire became known as metropolitans. The fourth-century ecumenical councils recognized the authority of the metropolitan. By the fifth century, the bishops of Rome, Constantinople, Alexandria and Antioch gained control of the churches in surrounding cities.They gradually became the heads of the regional churches, and were known as patriarchs (common father). Outside the Roman Empire, patriarchs were known as catholicos. There were four catholicates before the fifth century: the Catholicate of the East, the Catholicate of Armenia, the Catholicate of Georgia and the Catholicate of Albania. In Orthodox tradition, any apostolic and autonomous national church (often referred to as a local church) may call its head a catholicos, pope or patriarch. The archdeacons reigned from the fourth to the 16th centuries; in 1653, the archdeacon was elevated to bishop by the community as Thoma I.