Eusebius Pamphilus: 
De solemnitate Paschalis 

This work has never been translated into English, according to the bibliography in T.D.Barnes, Constantine and Eusebius, 1981.  

However Robert Stonehouse kindly translated chapter 1, and Matthew Johnson has kindly translated chapter 8, the only one that bears on the First Council of Nicaea.  Words in Italics are supplied by the translator as the sense requires.  The text used is that of J.-P.Migne in the Patrologia Graeco-Latina, Paris (1844+), volume 24, column 701:

EUSEBIUS OF CAESAREA'S "ON THE FEAST OF THE PASSOVER" 

1. It could well be opportune to take up yet again the subject of the Passover, handed down symbolically from above to the children of the Hebrews. At least at that point in time when the Hebrews, ritually performing the shadows of things to come, first carried out the festival of the [phasek? perhaps pascha, passover?], a young one was taken for them from the flock; this was a lamb or a sheep; and this they then sacrificed, themselves on their own account; and then with the blood they each first smeared the thresholds and door-posts of their own houses; in this way bloodying their thresholds and halls for turning away the destroyer. Using the flesh of the sheep for sustenance, and girding up their loins with a girdle, and partaking of the nourishment of unleavened loaves, and adding bitter herbs, they went from place to place, from the land of the Egyptians into the desert. So at least it was laid down for them to do at the time of the slaughter and eating of the sheep. Hence the departure from Egypt achieved for them the naming of the pass-over (offerings on crossing the border). 

But this happened to them as a sign; it was written on our account. And Paul informs us, when he makes plain from the old symbols the truth of what he says: For also Christ was sacrificed as our Passover. The cause of his sacrifice is witnessed by the Baptist, who says Behold the Lamb of God, that taketh away the sin of the world. For he handed over his saving body to death as a sacrifice to turn away all evils, which by way of purification took away the sin of all the universe. The cry of Isaiah shines from afar: He bears our sins and suffers for us.

[...]

8. When the Emperor beloved of God sat in the midst of the Council, and the dispute concerning Pascha was introduced, he said as he spoke above. And the three-quarters of all the bishops from all over the world prevailed, who opposed the Oriental bishops. For the North, together with the South and the West showed in harmony, taking position against those who looked to the ancient custom. But at last the Oriental bishops finished speaking, and thus there was one and the same feast of Christ. And thus they departed from those who slew the Lord, and all came to join in one opinion. For nature draws like to like. But if anyone should say "it is written 'on the third day of the feast of unleavened bread the disciples came together and said to the Lord, "where do you want us to prepare the Paschal feast?", and He sent two of them to someone to say to him, "I want to celebrate Pascha at your house"'", we say that this is not a commandment, but simply the history of the act at the time Our Savior suffered the Passion. For it is one thing to relate the ancient deed, and another to set up a law even to those who came after.

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Constructive feedback is welcomed to Roger Pearse.

Written 15th June 2001.