First appears as an Aryan sun-god in Sanskrit and Persian literature circa 1400 BCE. The cult was introduced into the Roman empire in the 1st century BCE.

Mithra was:

born of a virgin in a stable on the winter solstice--frequently December 25 in the Julian calendar (the emperor Aurelian declared December 25 to be the official birthday of Mithra, circa 270 CE)--attended by shepherds who brought gifts;

worshiped on Sundays;

shown with a nimbus, or halo, around his head;

said to take a last supper with his followers when he returned to his father;

believed not to have died, but to have ascended to heaven, whence it was believed he would return at the end of time to raise the dead in a physical resurrection for a final judgement, sending the good to heaven and the wicked to hell, after the world had been destroyed by fire;

to grant his followers immortal life following baptism.

Followers of Mithra:

followed a leader called a 'papa' (pope), who ruled from the Vatican hill in Rome;

celebrated the atoning death of a savior who has resurrected on a Sunday;

celebrated sacramenta (a consecrated meal of bread and wine), termed a Myazda (corresponding exactly to the Catholic Missa (mass), using chanting, bells, candles, incense, and holy water, in remembrance of the last supper of Mithra).

The emperor Constantine was a follower of Mithra until he declared December 25 the official birthday of Jesus in 313 CE and adopted the cult of Christianity as the state religion.

Basic sources for the study of Mithraism: