Here is a provocative, many might say highly inflammatory passage from the opening chapter of the book “The Return of the Light: Twelve Tales from Around the World for the Winter Solstice”
by Carolyn McVickar Edwards, now in its 5th Anniversary Edition.

“In Rome, in the first four hundred years of what we now call the common era, two major savior-religions vied for supremacy. The first savior, Mithra, the Unconquered Sun, was said to have been born of a mortal virgin on the old Brumalia, December 25th. Legend had his birth witnessed by shepherds and magi, and he performed a bevy of healing miracles, including raising the dead and causing the blind to see. Before dying and returning to heaven on what we call the vernal equinox, Mithra was said to have held a last supper with his twelve disciples who represented the twelve signs of the zodiac. The Roman military establishment hailed Mithraism for its rigid discipline and vivid battle imagery.

The Christian sun god, Jesus, Light of the World, had beliefs and rites so similar to that of Mithraism that St. Augustine declared that the priests of Mithra worshipped the same deity as he. Perhaps it was Chritianity’s relative softness, in those early days, towards the feminine, and its roots in Judaism, with its prediction of a messiah, that finally allowed Christ’s followers to seize the day. Mithraism thus became merely a tributary to the story that today shapes one of the world’s major religions.”

To represent a more acceptably Christian view, here’s an annotated paper by Ronald H. Nash which says the parallels drawn between Christianity and early Pagan “mystery” religions are greatly exaggerated.
It’s all fascinating reading.