The Edict of Milan, issued by two professing pagans, was the first royal proclamation in a series that would establish Catholic Christianity as the religion of empire,...
The Edict of Milan is ante-dated by the Edict of Toleration of the pagan Augustus Galerius, issued as a last-ditch political maneuver in 309-310. Here's the text in its entirety:
Among other arrangements which we are always accustomed to make for the prosperity and welfare of the republic, we had desired formerly to bring all things into harmony with the ancient laws and public order of the Romans, and to provide that even the Christians who had left the religion of their fathers should come back to reason ; since, indeed, the Christians themselves, for some reason, had followed such a caprice and had fallen into such a folly that they would not obey the institutes of antiquity, which perchance their own ancestors had first established; but at their own will and pleasure, they would thus make laws unto themselves which they should observe and would collect various peoples in diverse places in congregations. Finally when our law had been promulgated to the effect that they should conform to the institutes of antiquity, many were subdued by the fear of danger, many even suffered death. And yet since most of them persevered in their determination, and we saw that they neither paid the reverence and awe due to the gods nor worshipped the God of the Christians, in view of our most mild clemency and the constant habit by which we are accustomed to grant indulgence to all, we thought that we ought to grant our most prompt indulgence also to these, so that they may again be Christians and may hold their conventicles, provided they do nothing contrary to good order. But we shall tell the magistrates in another letter what they ought to do.
Wherefore, for this our indulgence, they ought to pray to their God for our safety, for that of the republic, and for their own, that the republic may continue uninjured on every side, and that they may be able to live securely in their homes.
This edict is published at Nicomedia on the day before the Kalends of May, in our eighth consulship and the second of Maximinus.
from Lactantius, De Mort. Pers. ch. 34, 35. Opera, ed. O. F. Fritzsche, II, P. 273. (Bibl. Patt. Ecc. Lat. XI, Leipzig, 1844.)