'Patriarch' is the ecclesiastical title dating from the 6th century and accorded to the Bishops of the five chief sees of Christendom; Rome, Alexandria, Antioch, Constantinople and Jerusalem.
Their jurisdiction extended over the adjoining territories and included certain important rights, such as the right to ordain the Metropolitans, that is, the Bishops of the principal sees within their jurisdiction and also to put them to trial when accused, and of hearing appeals against the judgements of these Metropolitans.
The earliest Bishops exercising such extensive powers were those of Rome (jurisdiction over Italy); Alexandria (jurisdiction over Egypt and Libya); and Antioch (jurisdiction over the large parts of Asia Minor). These three were recognised by the First Ecumenical Council of Nicaea (325 AD). But the Fourth Ecumenical Council at Chalcedon (451 AD) recognised as well Jerusalem and Constantinople. According to the 28th Canon of this Synod, a number of privileges were accorded to the see of Constantinople, by which it was raised to the position of second after Rome and jurisdiction was extended over Thrace, Asia and Pontus.
And though the Bishop of Rome protested against the importance and extent of the jurisdiction of the Archbishop of Constantinople, the latter became a little later Ecumenical Patriarch, that is, the first among the rest of the Patriarchates of the east.