Of his Zeal in Prayer, and the Honor he paid to the Feast of Easter
The emperor himself, as a sharer in the holy mysteries of our religion, would seclude himself daily at a stated hour in the innermost chambers of his palace; and there in solitary converse with his God, would kneel in humble supplication, and entreat the blessings of which he stood in need. But especially at the salutary feast of Easter, his religious diligence was redoubled; he fulfilled as it were the duties of a hierophant with every energy of his mind and body, and outvied all others in the zealous celebration of this feast. He changed, too, the holy night vigil into a brightness like that of day, by causing waxen tapers of great length to be lighted throughout the city: besides which, torches everywhere diffused their light, so as to impart to this mystic vigil a brilliant splendor beyond that of day. As soon as day itself returned, in imitation of our Saviour's gracious acts, he opened a liberal hand to his subjects of every nation, province, and people, and lavished abundant bounties on all.
Source: Life of Constantine (New Advent)