Library Eusebius of Caesarea Life of Constantine
Book 1, Chapter 6: That he was the Servant of God, and the Conqueror of Nations.
Thus, like a faithful and good servant, did he act and testify, openly declaring and confessing himself the obedient minister of the supreme King. And God immediately rewarded him, by making him ruler and sovereign, and victorious to such a degree that he alone of all rulers pursued a continual course of conquest, unsubdued and invincible, and through his trophies a greater ruler than tradition records ever to have been before. So dear was he to God, and so blessed; so pious and so fortunate in all that he undertook, that with the greatest facility he obtained the authority over more nations than any who had preceded him, and yet retained his power, undisturbed, to the very close of his life.
English translation by Ernest Cushing Richardson, in Nicene and Post-Nicene Fathers, Series II, Vol. I (eds. Philip Schaff and Henry Wace; Buffalo: Christian Literature Publishing Co., 1890). Public domain. Digital text via New Advent Church Fathers.