Quartodecimanism (literally "fourteenism") was the practice of fixing the celebration of Passover for Christians on the 14th day of Nisan in the Bible's Hebrew Calendar which, according to the Gospels, was the date Jesus was crucified in Jerusalem. This was the original method of fixing the date of the Passover. A controversy arose concerning whether it should also be a resurrection holiday, and whether it should instead be celebrated on Sunday, which is now the holiday that is called Easter.

Since the Bible's calendar is lunisolar and the Roman/Western calendar is only solar, it is difficult to calculate Nisan 14 in the western calendar without knowledge of how a lunisolar calendar system works. For various reasons, the Roman Catholics eventually chose to use a different method than the Jews and Jewish Christians had used for their Passover.

Quartodecimanism was popular among Christians in Asia Minor and it is generally believed that this was the method specifically preferred by the followers of John the Apostle, since it was advocated by Polycarp who was a disciple of either John the Apostle or John the Presbyter, assuming they are not the same person.

In the second century AD a

This difference resulted in the Apostolic Father Polycarp visiting Rome to settle the matter with Anicetus. In addition Polycrates of Ephesus and Irenaeus wrote in support of the Quartodecimans. Irenaeus also noted that "Anicetus conceded to Polycarp in the Church the celebration of the Eucharist, by way of showing him respect". However Anicetus' successor Victor I, the first Latin Bishop of Rome, excommunicated the Quartodecimans (then apparently led by Polycrates of Ephesus) for not adhering to the modified Paschal practices of Rome thereby causing a schism between the Church of Rome and those churches that observed the Quartodeciman. Despite this schism, the Quartodecimans Melito of Sardis and Polycarp, for example, are both recognized as Saints by both the Roman Catholic and Orthodox Churches.

Another recognized Catholic saint, Apollinaris, wrote, "There are, then, some who through ignorance raise disputes about these things (though their conduct is pardonable: for ignorance is no subject for blame -- it rather needs further instruction..)..The fourteenth day, the

In 325CE, the First Council of Nicaea came to a decision that the Church as a whole should use a unified system, which was the Roman one. The Catholic Epiphanius wrote in the mid-4th Century, "..the emperor..convened a council of 318 bishops..in the city of Nicea..They passed certain ecclesiastical canons at the council besides, and at the same time decreed in regard to the Passover that there must be one unanimous concord on the celebration of God's holy and supremely excellent day. For it was variously observed by people.." (Epiphanius. The Panarion of Epiphanius of Salamis, Books II and III (Sects 47-80), De Fide). Section VI, Verses 1,1 and 1,3. Translated by Frank Williams. EJ Brill, New York, 1994, pp.471-472). A Sunday date was selected, instead of Nisan 14 (which can fall on any day of the week). According to Eusebius' Life of Constantine, Book III chapter 18, the Roman emperor Constantine the Great stated: "Let us then have nothing in common with the detestable Jewish crowd; for we have received from our Saviour a different way."

The vast majority of Christians abide by this decision and observe Easter on a Sunday, although the method for calculating which Sunday varies. See also Computus.

Currently some smaller groups (some Sabbatarian Church of God groups, for example) have a Quartodeciman observance, and celebrate a Christian Passover on that day—they typically use unleavened bread and wine, but do not have a Passover Seder like the Jews do. (This Passover is not to be confused with the current Greek Orthodox "Pascha", which celebrates the resurrection of Christ.) The largest known Quartodeciman group, that specifically claims to trace its history through John, Polycarp, and Polycrates, is the Living Church of God (see its booklet, God's Church Through the Ages). Many critics, however, believe that the historical evidence cited is not firm enough to prove that claim of continuance. Jehovah's Witnesses celebrate the "Memorial of Christ's Death" or the "Lord's Evening Meal" on this day as well.