The Oxford Dictionary of the Christian Church, s.v. patriarch (ecclesiastical), also calls it "a title dating from the 6th century, for the bishops of the five great sees of Christendom". And Merriam-Webster's Encyclopedia of World Religions says: "Five patriarchates, collectively called the pentarchy, were the first to be recognized by the legislation of the emperor Justinian (reigned 527–565)".
"Quinisext Council". Encyclopædia Britannica. Retrieved 14 February 2010. "The Western Church and the Pope were not represented at the council. Justinian, however, wanted the Pope as well as the Eastern bishops to sign the canons. Pope Sergius I (687–701) refused to sign, and the canons were never fully accepted by the Western Church".
"The ancient customs of Egypt, Libya and Pentapolis shall be maintained, according to which the bishop of Alexandria has authority over all these places since a similar custom exists with reference to the bishop of Rome. Similarly in Antioch and the other provinces the prerogatives of the churches are to be preserved. In general the following principle is evident: if anyone is made bishop without the consent of the metropolitan, this great synod determines that such a one shall not be a bishop. If however two or three by reason of personal rivalry dissent from the common vote of all, provided it is reasonable and in accordance with the church's canon, the vote of the majority shall prevail" (Canon 6).
"Since there prevails a custom and ancient tradition to the effect that the bishop of Aelia is to be honoured, let him be granted everything consequent upon this honour, saving the dignity proper to the metropolitan" (Canon 7)
