In several of the autocephalous Eastern Orthodox churches and Eastern Catholic Churches, the patriarch or head bishop is elected by a group of bishops called the Holy Synod. For instance, the Holy Synod is a ruling body of the Georgian Orthodox Church. In Oriental Orthodoxy the Holy Synod is the highest authority in the church and it formulates the rules and regulations regarding matters of church organization, faith, and order of service. Early synods The principle of summoning a synod or council of ecclesiastical persons to discuss some grave question affecting the Church goes back to the very beginning of the Church's history. Since the day when the Apostles met at Jerusalem to settle whether Gentile converts were to keep the Old Law (Acts 15:6–29), it had been the custom to call together such gatherings as occasion required. Bishops summoned synods of their clergy, metropolitans and patriarchs summoned their suffragans, and then since 325 there was a succession of those greatest synods, representing the whole Catholic world, that are known as general councils. Eastern Orthodox Church Synod of the Ecumenical Patriarchate The Ecumenical Patriarchate is governed by the "Holy and Sacred Synod", developed from the "endemousa synod" (the "resident" synod), which consisted of the bishops living (even if only transiently) in or near Constantinople. It is presided over by the Patriarch of Constantinople and consists of twelve hierarchs, each of whom holds membership for a year, with half of them being replaced every six months. The Russian Holy Synod The Most Holy Synod or Most Holy Governing Synod () was a congregation of Orthodox church leaders in Russia. It was established by Peter the Great, Stefan Yavorsky and Feofan Prokopovich in January 1721 to replace the Patriarchate of Moscow. It was abolished following the February Revolution of 1917 and replaced with a restored patriarchate under Tikhon of Moscow. In modern Russia, the Holy Synod of the Russian Orthodox Church is the highest governing body of the Russian Orthodox Church between Sobors. It is headed by the Patriarch of Moscow and all the Rus'. The Greek Holy Synod The first other Orthodox Church to imitate the Russian Government by synod was that of Greece. The national assemblies of free Greece in 1822 and 1827 began the process of making their Church independent of the Ecumenical Patriarch of Constantinople. In 1833 the Greek Parliament formally rejected the patriarch's authority and set up