Or the other way around. The cult of Mithra became popular at the same time that Christianity was growing. In many ways, the baptism rite of the cult of Mithra probably came as an idea from Christianity. It certainly didn't predate it.
And when we say also that the Word, who is the first-birth45 of God, was produced without sexual union, and that He, Jesus Christ, our Teacher, was crucified and died, and rose again, and ascended into heaven, we propound nothing different from what you believe regarding those whom you esteem sons of Jupiter. For you know how many sons your esteemed writers ascribed to Jupiter: Mercury, the interpreting word and teacher of all; Aesculapius, who, though he was a great physician, was struck by a thunderbolt, and so ascended to heaven; and Bacchus too, after he had been torn limb from limb; and Hercules, when he had committed himself to the flames to escape his toils; and the sons of Leda, and Dioscuri; and Perseus, son of Danae; and Bellerophon, who, though sprung from mortals, rose to heaven on the horse Pegasus.Justin Martyr gives a point, by point, by point, accounting of the similarities between paganism and the 'new religion'. Its the same thing under a new name.But far be such a thought concerning the gods from every well-conditioned soul, as to believe that Jupiter himself, the governor and creator of all things, was both a parricide and the son of a parricide
Moreover, the Son of God called Jesus, even if only a man by ordinary generation, yet, on account of His wisdom, is worthy to be called the Son of God; for all writers call God the Father of men and gods. And if we assert that the Word of God was born of God in a peculiar manner, different from ordinary generation, let this, as said above, be no extraordinary thing to you, who say that Mercury is the angelic word of God. But if any one objects that He was crucified, in this also He is on a par with those reputed sons of Jupiter of yours, who suffered as we have now enumerated.
And if we even affirm that He was born of a virgin, accept this in common with what you accept of Perseus. And in that we say that He made whole the lame, the paralytic, and those born blind, we seem to say what is very similar to the deeds said to have been done by Aesculapius.