310 Vision of Apollo (Panegyric 6 310ad)
For on the day after that news had been received and you had undertaken the labor of double stages on your journey, you learnt that all the waves had subsided, and that the all-pervading calm which you had left behind had been restored. Fortune herself so ordered this matter that the happy outcome of your affairs prompted you to convey to the immortal gods what you had vowed at the very spot where you had turned aside toward the most beautiful temple in the whole world, or rather, to the deity made manifest, as you saw. For you saw, I believe, O Constantine, your Apollo, accompanied by Victory, offering you laurel wreaths, each one of which carries a portent of thirty years. For this is the number of human ages which are owed to you without fail—beyond the old age of a Nestor. And—now why do I say “I believe”?—you saw, and recognized yourself in the likeness of him to whom the divine songs of the bards had prophesied that rule over the whole world was due. And this I think has now happened, since you are, O Emperor, like he, youthful, joyful, a bringer of health and very handsome. Rightly, therefore, have you honored those most venerable shrines with such great treasures that they do not miss their old ones, any longer. Now may all the temples be seen to beckon you to them, and particularly our Apollo, whose boiling waters punish perjuries—which ought to be especially hateful to you.
Immortal gods, when will you grant that day on which this most manifestly present god, with peace reigning everywhere, may visit those groves of Apollo as well, both sacred shrines and steaming mouths of springs? Their bubbling waters cloudy with gentle warmth seem to wish to smile, Constantine, at your gaze, and to insert themselves within your lips.
You will certainly marvel at that seat of your divinity too, and its waters warmed without any trace of soil on fire, which has no bitterness of taste or exhalation, but a purity of draught and smell such as you find in icy springs. And there you will grant favors, and establish privileges, and at last restore my native place because of your veneration of that very spot.
8th Century Defense Sylvester (Later version of Life of Constantine)
“Those who dwell in the East are of corrupt belief, having Arian tendencies. But away with their vain and devilish opinions and their senseless views! The truth is not as they say, you foolish and senseless ones. It seems to me more truthful that he (Constantine) was baptized by the blessed Sylvester in elder Rome — which is also in accordance with the truth — and I accept this and believe it without hesitation as more secure and certain. I testify this to all: that the decrees said to have been issued in his name to Miltiades were fabricated by the Arians, seeking thereby to acquire prestige for themselves. These same Arians also wish to malign the most pious emperor Constantine, claiming he was unbaptized, which is both unbelievable and false. For if he had not been baptized, he would not have partaken of the divine mysteries at the Council of Nicaea, nor would he have assembled with the holy fathers — a thing which is absurd both to think and to say.”
Pagan Baptism Account (Sozomen 450)
I am not unaware [Sozomen writes] that the Hellenes tell how Constantine, after slaying certain members of his closest family circle and conniving at the death of his own son Crispus, repented and enquired of Sopater the philosopher, who was at that time the foremost representative of the succession (btacoXj) of Plotinus, concerning the means by which he might be purified. He [Sopater] replied that such sins admit no purification. The king, dismayed at this ban, happened to encounter some bishops, who promised that he would be cleansed from sin through repentance and baptism. These words found their mark, and he [Constantine] was delighted with them. He admired the doctrine [of the Church], and became a Christian, and led his subjects to the same faith
Another Pagan Acount
(Zosimus 500ad)
(content of this source is complete bullshit, says Pope Eusebius did baptism despite dying before 310 but he killed Crispus in 326, does indicate lower baptism date though)
When the whole empire devolved on Constantine alone, he no longer hid his natural malignity, but took the liberty of acting in all matters according to his own will. He was still celebrating the ancestral rites, though more out of necessity than respectfulness… When he came to Rome, he was full of arrogance, and thought fit to begin his impiety at home. Without any consideration for natural law he killed his son Crispus who, as I related before, had been considered worthy of the rank of Caesar, but had come under suspicion of having had intercourse with his step-mother, Fausta.
And when Constantine’s mother, Helena, was saddened by this atrocity and was inconsolable at the young man’s death, Constantine, as if to comfort her, applied a remedy worse than the disease: he ordered a bath to be overheated, and shut Fausta up in it until she was dead. Since he had these crimes on his conscience, and in addition had broken oaths, he approached the priests, seeking to expiate his sins; but they declared that there was no known method of purification capable of purging such impieties. A certain Egyptian 100 who had come to Rome from Iberia, and who had become familiar with the ladies of the palace, encountered Constantine and averred that the teaching of the Christians does away with all sinfulness and promises that as many of the impious as partake of it shall immediately be released from all sin. Constantine readily believed what he was told, deserted the ancestral religion and embraced that which the Egyptian proposed. On theoccasion of the traditional festival, during which it was required that the army ascend to the Capitol and accomplish the customary rites, Constantine took part in (exotvwvnoe) the festival because he feared the soldiers. But when the Egyptian sent him an apparition which unrestrainedly abused this ascent to the Capitol, he [Constantine] kept aloof from (ἀποστατήσας) the holy ritual, and incurred the hatred of the senate and the people. (11.29)
Julian the Apostate Account (pagan)
Caesares (362)
As for Constantine, he could not discover among the gods the model of his own career; but when he caught sight of Pleasure, who was not far off, he ran to her. She received him tenderly and embraced him, then after dressing him in raiment of many colours and otherwise making him beautiful, she led him away to Incontinence. There too he found Jesus, who had taken up his abode with her and cried aloud to all comers: ‘He that is a seducer, he that is a murderer, he that is sacrilegious and infamous, let him approach without fear! For with this water will I wash him and straightway make him clean. And though he should be guilty of those same sins a second time, let him but smite his breast and beat his head and I will make him clean again.’ To him Constantine came gladly, when he had conducted his sons forth from the assembly of the gods. But the avenging deities none the less punished both him and them for their impiety, and exacted the penalty for the shedding of the blood of their kindred, until Zeus granted them a respite for the sake of Claudius [Gothicus] and Constantius.
Contra Galilaeos (363)
Here is how [the apostle] Paul writes, about his followers, to those selfsame people: ‘Make no mistake: idolaters, adulterers, the effeminate, sodomites, thieves, misers, drunkards, slanderers, and swindlers, none of these will inherit the kingdom of God. And you are not unaware, my brothers, that you too were of this kind; but you have been washed clean, you have been sanctified in the name of Jesus Christ.’ [1 Cor. VI.9-I1] You see that he says that they too were of this kind, but they were sanctified and washed clean, having found water capable of washing and thoroughly purging them, and penetrating even to their soul. So this baptism, that neither relieves the leper of his leprosy, [nor cures] scabs or white leprosy [vitiligo alba, a mild form of the disease] or warts or gout or dysentery or dropsy or whitlow or any of the body’s failings small or great, will it drive out adulteries and swindlings and, in a word, all the soul’s transgressions?