How Constantine entertained the Bishops on the Occasion of His Vicennalia
About this time he completed the twentieth year of his reign. On this occasion public festivals were celebrated by the people of the provinces generally, but the emperor himself invited and feasted with those ministers of God whom he had reconciled, and thus offered as it were through them a suitable sacrifice to God. Not one of the bishops was wanting at the imperial banquet, the circumstances of which were splendid beyond description. Detachments of the bodyguard and other troops surrounded the entrance of the palace with drawn swords, and through the midst of these the men of God proceeded without fear into the innermost of the imperial apartments, in which some were the emperor's own companions at table, while others reclined on couches arranged on either side. One might have thought that a picture of Christ's kingdom was thus shadowed forth, and a dream rather than reality.
Source: Life of Constantine (New Advent)