[Excerpt adapted from Jacob R. Marcus, The Jew in the Medieval World, p. 105.]
Among the topics discussed at the Council of Nicea in 325 was when it was proper to observe the feast of Christ's resurrection (Easter). Two practices were being followed. Christians in the East ended a fast to mark Jesus' crucifixion on the first night of the Jewish Passover, on the 14th day of Nisan according to the Jewish calendar. They would break their fast with a Passover meal to commemorate Jesus' Last Supper. This practice was known as Quartodecimanism from the Latin word for fourteen. Christians in Rome ended their fast on the following Sunday. At issue was whether the Resurrection should be fixed on Sunday or associated with the 14th of Nisan, which since based on a lunar calendar could fall on any day of the week. Also involved was a desire to distinguish Jewish and Christian practices. Here the Emperor Constantine decides in favor of the Roman practice.
Constantinus Augustus to the Churches. . . .
At this meeting [the Council of Nicea] the question concerning the most holy day of the Paschal celebration [of the Resurrection] was discussed, and it was resolved by the united judgment of all present, that this feast ought to be kept by all and in every place on one and
the same day [Sunday]. For what can be more becoming or honorable to us than that this feast from which we date our hopes of immortality, should be observed unfailingly by all alike, according to one ascertained order and arrangement?
And first of all, it appeared an unworthy thing that in the celebration of this most holy feast we should follow the practice of the Jews, who have impiously defiled their hands with enormous sin, and are, therefore, deservedly afflicted with blindness of soul. For we have it in our power, if we abandon their custom, to prolong the due observance of this ordinance to future ages, by a truer order, which we have preserved from the very day of the Passion until the present time.
Let us then have nothing in common with the detestable Jewish crowd; for we have received from our Savior a different way. A course at once legitimate and honorable lies open to our most holy religion. Beloved brethren, let us with one consent adopt this course, and withdraw ourselves from all participation in their baseness. For their boast is absurd indeed, that it is not in our power without instruction from them to observe these things. . . .
In brief, that I may express my meaning in as few words as possible, it has been determined by the common judgment of all, that the most holy feast of Easter should be kept on one and the same day [Sunday]. For on the one hand a discrepancy of opinion on so sacred aquestion is unbecoming, and on the other it is surely best to act on a decision which is free from strange folly and error. . . .
God preserve you, beloved brethren!