Eusebius on the Nicean Council...

"Detachments of the body-guard and troops surrounded the entrance of the palace with drawn swords, and through the midst of them the men of God proceeded without fear into the innermost of the Imperial apartments, in which some were the Emperor's companions at table, while others reclined on couches arranged on either side. One might have thought that a picture of Christ's kingdom was thus shadowed forth, and a dream rather than reality." - Eusebius, Vita Constantini, 3:15

"Eleven years afterwards, a more numerous and celebrated assembly was convened at Nice in Bithynia, to extinguish, by their final sentence, the subtle disputes which had arisen in Egypt on the subject of the Trinity. Three hundred and eighteen bishops obeyed the summons of their indulgent master; the ecclesiastics of every rank, and sect, and denomination, have been computed at two thousand and forty-eight persons; the Greeks appeared in person; and the consent of the Latins was expressed by the legates of the Roman pontiff. The session, which lasted about two months, was frequently honored by the presence of the emperor. Leaving his guards at the door, he seated himself (with the permission of the council) on a low stool in the midst of the hall. Constantine listened with patience, and spoke with modesty: and while he influenced the debates, he humbly professed that he was the minister, not the judge, of the successors of the apostles, who had been established as priests and as gods upon earth." - Eusebius, Vita Constantini, 7

On the synthesis of Christianity and Sol Invictus:

"A third-century mosaic from the Mausoleum of the Julii underneath present-day St. Peter's in Rome actually portrays Jesus as Sol Invictus, driving the horses of the sun's chariot. That Constantine himself mixed Christianity and the Sol Invictus cult is clear form a second commemorative medallion issued by him within two years of the first, on which he represented himself with a Chi-Rho monogram on his helmet, and with a leaping Sol chariot below. "It was only when he was approaching death that he asked for, or was accepted for, Christian baptism. As was still the custom, he received this naked, thereafter renouncing forever the purple of his imperial rank." - Ian Wilson, Jesus, The Evidence

Letter from Pliny to the Emperor Trajan on the Christian dilemma:

It is my practice, my lord, to refer to you all matters concerning which I am in doubt. For who can better give guidance to my hesitation or inform my ignorance? I have never participated in trials of Christians. I therefore do not know what offenses it is the practice to punish or investigate, and to what extent. And I have been not a little hesitant as to whether there should be any distinction on account of age or no difference between the very young and the more mature; whether pardon is to be granted for repentance, or, if a man has once been a Christian, it does him no good to have ceased to be one; whether the name itself, even without offenses, or only the offenses associated with the name are to be punished.

Meanwhile, in the case of those who were denounced to me as Christians, I have observed the following procedure: I interrogated these as to whether they were Christians; those who confessed I interrogated a second and a third time, threatening them with punishment; those who persisted I ordered executed. For I had no doubt that, whatever the nature of their creed, stubbornness and inflexible obstinacy surely deserve to be punished. There were others possessed of the same folly; but because they were Roman citizens, I signed an order for them to be transferred to Rome.

Soon accusations spread, as usually happens, because of the proceedings going on, and several incidents occurred. An anonymous document was published containing the names of many persons. Those who denied that they were or had been Christians, when they invoked the gods in words dictated by me, offered prayer with incense and wine to your image, which I had ordered to be brought for this purpose together with statues of the gods, and moreover cursed Christ--none of which those who are really Christians, it is said, can be forced to do--these I thought should be discharged. Others named by the informer declared that they were Christians, but then denied it, asserting that they had been but had ceased to be, some three years before, others many years, some as much as twenty-five years. They all worshipped your image and the statues of the gods, and cursed Christ.

They asserted, however, that the sum and substance of their fault or error had been that they were accustomed to meet on a fixed day before dawn and sing responsively a hymn to Christ as to a god, and to bind themselves by oath, not to some crime, but not to commit fraud, theft, or adultery, not falsify their trust, nor to refuse to return a trust when called upon to do so. When this was over, it was their custom to depart and to assemble again to partake of food--but ordinary and innocent food. Even this, they affirmed, they had ceased to do after my edict by which, in accordance with your instructions, I had forbidden political associations. Accordingly, I judged it all the more necessary to find out what the truth was by torturing two female slaves who were called deaconesses. But I discovered nothing else but depraved, excessive superstition.

I therefore postponed the investigation and hastened to consult you. For the matter seemed to me to warrant consulting you, especially because of the number involved. For many persons of every age, every rank, and also of both sexes are and will be endangered. For the contagion of this superstition has spread not only to the cities but also to the villages and farms. But it seems possible to check and cure it. It is certainly quite clear that the temples, which had been almost deserted, have begun to be frequented, that the established religious rites, long neglected, are being resumed, and that from everywhere sacrificial animals are coming, for which until now very few purchasers could be found. Hence it is easy to imagine what a multitude of people can be reformed if an opportunity for repentance is afforded.

Trajan's responce to Pliny:

You observed proper procedure, my dear Pliny, in sifting the cases of those who had been denounced to you as Christians. For it is not possible to lay down any general rule to serve as a kind of fixed standard. They are not to be sought out; if they are denounced and proved guilty, they are to be punished, with this reservation, that whoever denies that he is a Christian and really proves it--that is, by worshiping our gods--even though he was under suspicion in the past, shall obtain pardon through repentance. But anonymously posted accusations ought to have no place in any prosecution. For this is both a dangerous kind of precedent and out of keeping with the spirit of our age.

Similar declarations at communion:

"He who will not eat of my body, nor drink of my blood so that he may be one with me and I with him, shall not be saved." - Mithraic Communion (M. J. Vermaseren, Mithras, The Secret God)

"And as they were eating, Jesus, having taken bread, when he had blessed, broke [it], and gave [it] to them, and said, Take [this]: this is my body. And having taken [the] cup, when he had given thanks, he gave [it] to them, and they all drank out of it. And he said to them, This is my blood, that of the [new] covenant, that shed for many." - Mark 14:22-26

More similarities:

"But you are not to be called rabbi, for you have one teacher, and you are all brethren. And call no man your father on earth, for you have one Father, who is in heaven. Neither be called masters, for you have one master, the Christ." - Matthew 23:8-10

"The Mithraic Holy father wore a red cap and garment and a ring, and carried a shepherd's staff. The Head Christian adopted the same title and outfitted himself in the same manner. Christian priests, like Mithraic priests, became 'Father', despite Jesus' specific proscription of the acceptance of such a title (Matthew 23:9). That Jesus had been repudiating, not the Mithraists with whom he was unfamiliar, but the Sanhedrin, whose President was styled Father, is hardly relevant. "Mithra's bishops wore a mithra, or miter, as their badge of office. Christian bishops also adopted miters. Mithraists commemorated the sun-god's ascension by eating a mizd, a sun-shaped bun embossed with the sword (cross) of Mithra. The hot cross bun and the mass were likewise adapted to Christianity. The Roman Catholic mizd/mass wafer continues to retain its sun-shape, although its Episcopal counterpart does not. "All Roman Emperors from Julius Caesar to Gratian had been pontifex maximus, high priest of the Roman gods. When Theodosius refused the title as incompatible with his status as a Christian, the Christian bishop of Rome picked it up. Magi, priests of Zarathustra, wore robes that featured the sword of Mithra. Identical robes are worn by Christian priests to this day." - William Harwood, Mythologies Last Gods: Yahweh and Jesus

"The liturgy of the Eucharist that John prescribes to the converted in being 'born again' is necessary 'so that the speaker might gaze upon the immortal beginning (Jesus) with the immortal (Holy) spirit ... and be born again in thought.' [Grese]." "Some modern Christian believers are familar with this concept of being born again through a spirit and regard it as unique to Christianity. The just-quoted text however is from the pagan Mithras Liturgy, a guidebook of sorts that assists in the Eucharist and prepares the sojourner for his heavenly journey. It advises the seeker of the Sun-god (father of Mithras) to pray saying:" - James Still, "The Gospel of John and the Hellenization of Jesus"

"[F]irst beginning of my beginning, ...spirit of spirit, the first spirit in me, ...now if it be your will, ...give me over to immortal birth and, following that, to my underlying nature, so that, after the present need which is pressing me exceedingly, I may gaze upon the immortal beginning with the immortal spirit, that I may be born again in thought." - Mithras Liturgy

Paulian appeal to Mithraicists, admitting to the blessing effects of the Mithraic Baptism: