What Were They Singing in the 4th Century?

At the Lamb's high feast we sing.

Last Supper - public domain

Praise to our victorious King,
Who has washed us in the tide
Flowing from his pierced side;
Praise we him, whose love divine
Gives his sacred blood for wine,
Gives his body for the feast,
Christ the Victim, Christ the Priest.

Where the Paschal blood is poured,
Death's dark angel sheaths his sword;
Israel's hosts triumphant go
Through the wave that drowns the foe.
Praise we Christ, whose blood was shed,
Paschal Victim, Paschal Bread;
With sincerity and love
Eat we Manna from above.

(4th century hymn translated from Latin - public domain)

Even the music of the Early Church speaks of the Real Presence. Consider the words ... and believe.

What Were They Singing in the 4th Century?