As the Jewish Passover feast can begin either on the Tuesday, Thursday, Saturday or Sunday after the first cyclical Full Moon following the spring equinox, it tends to fall before the Easter Sunday observed by the Christians. At first, when both Jews and Christians were only minority groups within the Roman Empire, this was of no importance, but when Christianity became the Roman state religion after the mid-4th century this often brought the Jews in problems with the Roman authorities when they were observed to hold their celebrations while the Christians were still fasting.
According to the Secret History of Procopius of Caesarea (Anecdota [Historia Arcana], ch. 28.16-19):
[The emperor Justinian I (reigned 527-565)] also took pains to abolish the laws which the Hebrews honour. If it ever happened, for instance, that the year in its recurring rounds brought on the Feast of Passover before the festival of the Christians, he would not allow the Jews to celebrate this at the proper time, not to make any offering to God at that feast, nor to perform any of the rites customary among them. And many of them used to be brought to trial as having tasted the flesh of lambs at this time by those who were in a position of authority, and these punished them by heavy fines, arraigning them for violation of the laws of the State.
Since AD 358/359 (AM 4119), the traditional year of the promulgation of the Jewish rabbinic calendar by Hillel II, there have been 24 coincidences between the first day of the Jewish Passover feast (15 Nisan) and the Alexandrian (later the Dionysian) Easter Sunday.
|367||4127||1 April||499||4259||11 April|
|370||4130||28 March||519||4279||31 March|
|374||4134||13 April||523||4283||16 April|
|394||4154||2 April||536||4296||23 March|
|401||4161||14 April||543||4303||5 April|
|414||4174||22 March||563||4323||25 March|
|418||4178||7 April||570||4330||6 April|
|421||4181||3 April||590||4350||26 March|
|441||4201||23 March||594||4354||11 April|
|445||4205||8 April||614||4374||31 March|
|465||4225||28 March||743||4503||14 April|
|496||4256||14 April||783||4543||23 March|
Only twice, on 8 April 475 (AM 4235) and on 28 March 495 (AM 4255), did the first day of the Jewish Passover feast follow Easter Sunday (in both cases by two days). In all other years the first day of the Jewish Passover feast occurred before Easter Sunday.
Note that the coincidence rate remained fairly constant until the 6th century, after which it dropped sharply and after AD 783 no further coincidences have occurred. This is due to the slowly increasing offset between the Jewish and the Julian spring equinox dates. This fact was later interpreted by some calendar historians to have been an intentional feature of the Dionysian Easter tables, but there appears to be no evidence for this.
Note: The above calculations are based on the somewhat questionable assumption that during the Late Roman and Early Byzantine period the Jewish rabbinic calendar was already identical with the present rabbinic calendar.