The Pentarchy
πενταρχία — pentarchia · pen-tar-KHEE-ah
In brief
The pentarchy — "rule of five" — is the ancient ordering of the Church's five senior patriarchates: Rome, Constantinople, Alexandria, Antioch, and Jerusalem, in that traditional order of honor. In the age of the councils these five great sees were understood to hold a shared responsibility for the whole Church. It was a model of communion among equals, not a pyramid: the pentarchy never meant that any one see, Rome included, ruled the other four.
The five sees
Three of the five were ancient beyond memory. Rome, Alexandria, and Antioch were already recognized as the Church's leading centers by the First Ecumenical Council at Nicaea (325, canon 6), each honored as the mother-church of its region. To these two more were added. Constantinople, the new imperial capital, was given the rank of honor next after Rome by the Second Ecumenical Council in 381 — "because Constantinople is New Rome." Jerusalem, small but holy as the place of the Lord's death and rising, was raised to the dignity of a patriarchate by the Fourth Ecumenical Council at Chalcedon (451).
By the sixth century their order of precedence had settled into the form the Church still recites: Rome, Constantinople, Alexandria, Antioch, Jerusalem. This was an order of honor, not of power — a way of knowing who was named first, not who could command the rest.
A picture of the whole Church
The emperor Justinian gave the arrangement legal shape in his laws, and later Byzantine writers turned it into a theory: as the body has five senses, so Christ's Body is governed by five patriarchs in concord, each caring for his own vast territory while all remain in one communion of faith. No question touching the whole Church could be settled by one see alone; it belonged to all of them together, and finally to an Ecumenical Council.
This is why the Orthodox understanding of Rome's ancient primacy is a primacy of honor — first among equals — rather than a universal jurisdiction. Within the pentarchy the bishop of Rome was named first and greatly revered, but he was one of five brother-patriarchs, not their head or their judge.
What the theory could and could not carry
The pentarchy was never the Church's only structure — the faith had spread far beyond these five cities, and whole peoples would later receive their own self-governing churches. And it proved fragile. The Christological divisions after Chalcedon (451) and the Arab conquests of the seventh century left Alexandria, Antioch, and Jerusalem diminished and, in time, under Muslim rule. Rome departed from the communion in the schism between East and West.
What survives is not a working government of five but a memory and an order of honor. The four ancient Eastern sees remain, and Orthodox Christians still name them with reverence; among them the Ecumenical Patriarch of Constantinople holds the primacy of honor. The pentarchy is best understood as one historic expression of a permanent Orthodox conviction: that the Church is ruled not by a single head but by bishops in council and communion.