One of the great debates of church history is little known among non-scholars–the Quartodeciman Controversy. This was the debate that raged for nearly 200 years about when Easter should be celebrated. The early Church practice was to observe it on 14 Nisan (hence, Quartodeciman), and this dominated in the east; the Roman custom developed to observe it always on a Sunday, and Rome’s lead caused this to become universal.
Wikipedia has a helpful summary. Polycarp, a disciple of John, advocated for 14 Nisan before Anicetus, Bishop of Rome, and remained in communion; later generations were not so fortunate, and were excommunicated by Victor I–who was promptly reproached by other bishops, including Irenaeus (see Eusebius). The controversy didn’t die down; in 325 Nicea addressed it, and Emperor Constantine wrote a letter to those who didn’t attend the council to let them know about the Easter discussion. Constantine’s letter is a painful read. His bottom line (and, apparently, the council’s) is that we should not do what the Jews do. In other words, anti-Judaism was a major reason for the suppression of the original practice of celebrating the Pasch on 14 Nisan.
It was, in the first place, declared improper to follow the custom of the Jews in the celebration of this holy festival, because, their hands having been stained with crime, the minds of these wretched men are necessarily blinded. By rejecting their custom, we establish and hand down to succeeding ages one which is more reasonable, and which has been observed ever since the day of our Lord’s sufferings. Let us, then, have nothing in common with the Jews, who are our adversaries.