"A question of no small importance arose at that time [i.e. the time of Pope Victor I, about A.D. 190]. The dioceses of all Asia, according to an ancient tradition, held that the fourteenth day of the moon [of Nisan], on which day the Jews were commanded to sacrifice the lamb, should always be observed as the feast of the life-giving pasch (epi tes tou soteriou Pascha heortes ἐπὶ ταῖς τοῦ σωτηρίου Πάσχα ἑορταῖς), contending that the fast ought to end on that day, whatever day of the week it might happen to be. However it was not the custom of the churches in the rest of the world to end it at this point, as they observed the practice, which from Apostolic tradition has prevailed to the present time, of terminating the fast on no other day than on that of the Resurrection of our Saviour."

Irenaeus records the diversity of practice regarding Easter that had existed at least from the time of Pope Sixtus I (c. 120). He recorded Polycarp, the bishop of Smyrna, observing the fourteenth day of the moon, whatever day of the week that might be, following a tradition which he claimed to have derived from John the Apostle.

Around 195, Pope Victor I, attempted to excommunicate the Quartodecimans, turning the divergence of practice into a full-blown ecclesiastical controversy. According to Eusebius, synods were convened and letters were exchanged, but in the end, having overstepped his mark, Victor, the Bishop of Rome, was rebuked and had to back down.

"But this did not please all the bishops. And they besought him to consider the things of peace, and of neighborly unity and love. Words of theirs are extant, sharply rebuking Victor.

Among them was Irenæus, who, sending letters in the name of the brethren in Gaul over whom he presided, maintained that the mystery of the resurrection of the Lord should be observed only on the Lord’s day. He fittingly admonishes Victor that he should not cut off whole churches of God which observed the tradition of an ancient custom."

First Council of Nicaea in 325

The First Council of Nicaea (A.D. 325) declared that Easter was always to be held on a Sunday, and was not to coincide with a particular phase of the moon, which might occur on any day of the week. However, a new dispute arose as to the determination of the Sunday itself, since Sundays can occur on any date of the month. Shortly before the Nicean Council, in 314, the Provincial Council of Arles in Gaul had maintained that the Lord's Pasch should be observed on the same day throughout the world and that each year the Bishop of Rome should send out letters setting the date of Easter.[2]

The Syriac Christians always held their Easter festival on the Sunday after the Jews kept their Pesach. On the other hand, at Alexandria, and seemingly throughout the rest of the Roman Empire, the Christians calculated the time of Easter for themselves, paying no attention to the Jews. In this way the date of Easter as kept at Alexandria and Antioch did not always agree. The Jewish communities in some places, possibly including Antioch, used methods of fixing their month of Nisan that sometimes put the 14th day of Nisan before the spring equinox. The Alexandrians, on the other hand, accepted it as a first principle that the Sunday to be kept as Easter Day must necessarily occur after the equinox.

The Council of Nicaea ruled that all churches should follow a single rule for Easter, which should be computed independently of the Jewish calendar, as at Alexandria. However, it did not make any explicit ruling about the details of the computation, and it was several decades before the Alexandrine computations stabilized into their final form, and several centuries beyond that before they became normative throughout Christendom.

Synod of Whitby in 664

The Roman missionaries coming to Britain in the time of Pope Gregory I (590–604) found the British Christians, who had been evangelized by Irish missionaries from the north, adhering to a different system of Easter computation from that used in the Mediterranean basin. This system, on the evidence of Bede, fixed Easter to the Sunday falling in the seven-day period from the 14th to the 20th of its lunar month, according to an 84-year cycle.[3] The limits of Nisan 14 – Nisan 20 are corroborated by Columbanus.[4] The method used by the Roman Church was Nisan 15 – Nisan 21.[5] The 84-year cycle, the lunar limits, and an equinox of March 25 also receive support from McCarthy's analysis of Padua, Biblioteca Antoniana, MS I.27.[6] Any of these features alone could have led to occasional discrepancies from the date of Easter as computed by the Alexandrine method.

This 84-year cycle (called the latercus) gave way to the Alexandrine computus in stages. The Alexandrine computus may have been adopted in parts of the south of Ireland in the first half of the 7th century.[7] Among the northern English, the use of the Alexandrine computus over the Brittano-Irish cycle was decided at the Synod of Whitby in AD 664.[8] The Alexandrine computus was finally adopted by the Irish colonies in northern Britain in the early 8th century.[9]

Several attempts have sought to achieve a common method for computing the date of Easter. In 1997 the World Council of Churches proposed a reform of the method of determining the date of Easter[10] at a summit in Aleppo, Syria: Easter would be defined as the first Sunday following the first astronomicalfull moon following the astronomical vernal equinox, as determined from the meridian of Jerusalem. The reform would have been implemented starting in 2001, since in that year the Eastern and Western dates of Easter would coincide. This reform has not been implemented.