Speaking about Easter or Passover, we have to mention the controversy about the timing. This strife was finally settled at the Council at Nicaea in AD 325, where it was agreed to celebrate the resurrection of Christ on a Sunday whatever the date. In Wikipedia we read:
"The second stage in the Easter controversy centers around the First Council of Nicaea (A.D. 325). Granted that the great Easter festival was always to be held on a Sunday, and was not to coincide with a particular age of the moon, which might occur on any day of the week, 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." 
First time we hear of divergences in this question is around the AD 120. According to the church historian Eusebius of Caesarea (d. 339) Polycarp (d. 155), the bishop of Smyrna and a companion of Papias, who had known the Apostle John, had travelled to Rome to convince the Pope that the right thing was to commemorate the death of Jesus on the 14th of the lunar month Nisan. In Rome, and in the West, Sunday had been chosen instead to celebrate the resurrection of Christ.
Quoting Irenaeus, bishop of Lyon, (d. c. 202) Eusebius writes:
"And when the blessed Polycarp was at Rome in the time of [Pope] Anicetus, and they disagreed a little about certain other things, they immediately made peace with one another, not caring to quarrel over this matter. For neither could Anicetus persuade Polycarp not to observe what he had always observed with John the disciple of our Lord, and the other apostles with whom he had associated; neither could Polycarp persuade Anicetus to observe it as he said that he ought to follow the customs of the presbyters that had preceded him." 
Interestingly, Polycarp based the celebration of the 14th of Nisan on the practise of the apostles. This would be in harmony with the words of Jesus when he instituted the Lords Supper: "Then he took a loaf of bread, gave thanks, broke it in pieces, and handed it to them, saying, 'This is my body, which is given for you. Keep on doing this in memory of me.'" 
Polycarp and Anicetus parted in disagreement, but in peace. But this was not the end of the controversy. A footnote to Eusebius has this to tell us:
"About 170 a.d. the controversy broke out again in Laodicea, the chief disputants being Melito of Sardis and Apolinarius of Hierapolis. In this controversy Melito advocated the traditional Asiatic custom of observing the fourteenth day, while Apolinarius opposed it." 
Many years after the death of Polycarp, the problem was up again. Eusebius writes:
"A question of no small importance arose at that time. For the parishes of all Asia, as from an older tradition, held that the fourteenth day of the moon, on which day the Jews were commanded to sacrifice the lamb, should be observed as the feast of the Saviour’s passover. It was therefore necessary to end their fast on that day, whatever day of the week it should happen to be. But it was not the custom of the churches in the rest of the world to end it at this time, 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." 
Polycrates, the Bishop of Ephesus where the Apostle John had died a hundred years earlier, went to Rome to see Pope Victor (d. 199). Eusebius quotes Polycrates addressing Victor with these words:
"We observe the exact day; neither adding, nor taking away. For in Asia also great lights have fallen asleep, which shall rise again on the day of the Lord’s coming, when he shall come with glory from heaven, and shall seek out all the saints. Among these are Philip, one of the twelve apostles, who fell asleep in Hierapolis; and his two aged virgin daughters, and another daughter, who lived in the Holy Spirit and now rests at Ephesus; and, moreover, John, who was both a witness and a teacher, who reclined upon the bosom of the Lord, and, being a priest, wore the sacerdotal plate.
"He fell asleep at Ephesus.
"And Polycarp in Smyrna, who was a bishop and martyr; and Thraseas, bishop and martyr from Eumenia, who fell asleep in Smyrna.
"Why need I mention the bishop and martyr Sagaris who fell asleep in Laodicea, or the blessed Papirius, or Melito, the Eunuch who lived altogether in the Holy Spirit, and who lies in Sardis, awaiting the episcopate from heaven, when he shall rise from the dead?
"All these observed the fourteenth day of the passover according to the Gospel, deviating in no respect, but following the rule of faith. And I also, Polycrates, the least of you all, do according to the tradition of my relatives, some of whom I have closely followed. For seven of my relatives were bishops; and I am the eighth. And my relatives always observed the day when the people put away the leaven. I, therefore, brethren, who have lived sixty-five years in the Lord, and have met with the brethren throughout the world, and have gone through every Holy Scripture, am not affrighted by terrifying words. For those greater than I have said ‘We ought to obey God rather than man.’” 
It seems, therefore, that Christians in the East, Antioch included, continued to observe the 14th of the lunar month of Nisan as the day of Jesus' death.
Interestingly, there was never any disagreement between the eastern and western churches about the date of Jesus' resurrection. All of them admitted that it fell on Sunday, Nisan 16. The issue was about which day to observe. In the words of Catholic Encyclopedia:
"The question thus debated was therefore primarily whether Easter was to be kept on a Sunday, or whether Christians should observe the Holy Day of the Jews, the fourteenth of Nisan, which might occur on any day of the week. Those who kept Easter with the Jews were called Quartodecimans or terountes (observants); but even in the time of Pope Victor this usage hardly extended beyond the churches of Asia Minor." 
That the Sunday celebration of western churches was for the Lord's resurrection is clear enough. But what did the Quartodecimans, or the eastern churches do on Nisan 14?
These words of Eusebius seem to clarify the matter:
"A question of no small importance arose at that time. For the parishes of all Asia, as from an older tradition, held that the fourteenth day of the moon, on which day the Jews were commanded to sacrifice the lamb, should be observed as the feast of the Saviour’s Passover." 
Keeping in mind that the 14th of Nisan started at sunset on Thursday and continued until Friday evening, it is reasonable to believe that the ancient custom consisted of celebrating the Lord's Supper (also called Eucharist) in commemoration of the death of Christ. As a footnote to Eusebius states:
"The Asiatic churches, in observing the fourteenth of Nisan, were commemorating the last passover feast and the death of the paschal Lamb." 
The question now is how this dissent came about. The standpoint of the eastern churches is clear: they just did what the scriptures apostles had told them to do. The West chose to celebrate the resurrection instead of the death of Christ, claiming that this was what the apostles Peter and Paul had told them to do. However, both Peter and Paul are connected to the eastern city of Antioch as well, and Paul travelled extensively in Asia Minor, where the practice of the Quartodecimans was widespread.
One cannot help wondering if the western churches changed an ancient custom simply to disassociate themselves from the Jews, who celebrated their Passover on the same day Christ instituted the Lord's Supper.
________1. "Easter controversy," Wikipedia, accessed April 4, 2013, http://en.wikipedia.org/wiki/Easter_controversy.
2. Papias is reported to have said:
"I will not hesitate to add also for you to my interpretations what I formerly learned with care from the Presbyters and have carefully stored in memory, giving assurance of its truth. For I did not take pleasure as the many do in those who speak much, but in those who teach what is true, nor in those who relate foreign precepts, but in those who relate the precepts which were given by the Lord to the faith and came down from the Truth itself. And also if any follower of the Presbyters happened to come, I would inquire for the sayings of the Presbyters, what Andrew said, or what Peter said, or what Philip or what Thomas or James or what John or Matthew or any other of the Lord's disciples, and for the things which other of the Lord's disciples, and for the things which Aristion and the Presbyter John, the disciples of the Lord, were saying. For I considered that I should not get so much advantage from matter in books as from the voice which yet lives and remains." - Michael William Holmes, The Apostolic Fathers in English (Baker Academic, 2006) 309, quoted at Wikipedia, "Papias," accessed on April 6, 2013.
3. Eusebius Pamphilius, ed. Philip Shaff, Church History, Life of Constantine, Oration in Praise of Constantine, (New York:Christian Literature Publishing Co., 1890 493 (Christian Classics Ethereal Library, www.ccel.org/ccel/schaff/npnf201.html ).
4. Luke 22:19, International Standard Version (© 2012).
5. Eusebius Pamphilius, Church History, Life of Constantine, Oration in Praise of Constantine, 487n1687.
6. Ibid., 487-88.
7. Ibid., 489-90.
8. "Easter Controversy," Catholic Encyclipedia (New Advent), accessed April 6, 2013, http://www.newadvent.org/cathen/05228a.htm.
9. Eusebius Pamphilius, Church History, Life of Constantine, Oration in Praise of Constantine,485.
10. Ibid., 409n1702.
11. Thus Early Church History to A. D. 451, Lesson 10, Page1, accessed April 6, 2013, http://www.parsonsapple.com/church%20history/Lecture10.pdf.