With the emerging of Zoroastrianism, he was reduced to the status of Yazata. In the Avesta he was portrayed as having ten thousand ears and eyes, and he rides in a chariot pulled by white horses. In the 4 century BCE his popularity rose and again he held a high position in the Persian pantheon. Eventually his cult spread beyond Iran and Asia Minor and gradually became a mystery cult. The ascetic religion of Mithraism (to which only men were allowed) became increasingly popular among the Roman soldiers around 100 CE and at that time Mithra was known in Rome as 'Deus sol invictus' ("the unconquered sun"). Even the Roman emperor Commodus was initiated into Mithra's cult. When Constantine the Great was converted to Christianity in 312 CE, Mithraism started to decline and after a temporary revival under Julius the Apostate (331-363) the cult disappeared for good.
Mithra was worshipped in Mithraea, artificially constructed caves that represented his birth-cave. The ceiling looked like the starry sky and at the sides benches where placed for the ritual meals. In the center of the Mithraea was a niche which held a relief of the god, dressed in Phrygian clothing (short tunic and cloak, long trousers and a hat with a curled tip), who kills a bull. The Mithraea were spread all over the Roman empire and some 50 of these caves still exist in Rome today.
He is also known as Mitra in the Indian Veda.