Mithraism, the worship of Mithra, the Iranian god of the sun, justice, contract, and war in pre-Zoroastrian Iran. Known as Mithras in the Roman Empire during the 2nd and 3rd centuries ce, this deity was honoured as the patron of loyalty to the emperor. After the acceptance of Christianity by the emperor Constantine in the early 4th century, Mithraism rapidly declined. Before ancient religious reformer Zarathustra (Greek name Zoroaster) gained influence in the region during the 6th century bce, the Iranians had a polytheistic religion, and Mithra was the most important of their gods. First of all, he was the