Nicene and Post-Nicene Fathers, Ser. II, Vol I:
The Life of Constantine with Orations of Constantine and Eusebius.: Chapter IX

p. 543 Chapter IX.—Letter of Constantine Augustus to Sapor, King of the Persians, containing a truly Pious Confession of God and Christ.

Copy of his Letter to the King of Persia.

“By keeping the Divine faith, I am made a partaker of the light of truth: guided by the light of truth, I advance in the knowledge of the Divine faith. Hence it is that, as my actions themselves evince, I profess the most holy religion; and this worship I declare to be that which teaches me deeper acquaintance with the most holy God; aided by whose Divine power, beginning from the very borders of the ocean, I have aroused each nation of the world in succession to a well-grounded hope of security; so that those which, groaning in servitude to the most cruel tyrants and yielding to the pressure of their daily sufferings, had well nigh been utterly destroyed, have been restored through my agency to a far happier state. This God I confess that I hold in unceasing honor and remembrance; this God I delight to contemplate with pure and guileless thoughts in the height of his glory.