Mithra

Mithra (Avestan Miθra, later Mihr) is one of the oldest gods of the Iranian world, cognate with the Vedic Mitra and, like him, the divinity of the contract — the binding agreement, the sworn word, loyalty kept. His name is itself a common noun for 'covenant'. He is 'he of wide pastures', the god of the broad light of day and of the sun that sees everything; and because he sees everything he is the terrible enemy of the mithra-druj, the man who lies to Mithra by breaking his oath. The great Avestan hymn to him, the Mihr Yašt (Yasht 10), shows him driving across the sky in his chariot, watchful and swift to punish the faithless.

Mithra binds naturally to the Achaemenid ideology of Truth against the Lie: to break faith is to fall to the Lie, and Mithra is the god before whom oaths of loyalty were sworn. His hold on Persian life shows in the flood of names compounded with his — Mithradates, 'given by Mithra' — and in the royal festival the Greeks called the Mithrakana (later Mehregān).

In the royal inscriptions

Neither Darius nor Xerxes names any god but Ahura Mazdā (and 'the other gods'). Mithra appears by name only later, in the inscriptions of Artaxerxes II and III, invoked as part of a triad — 'may Ahuramazda, Anāhitā and Mithra protect me'. Whether this marks a genuine religious change or simply the surfacing into royal epigraphy of gods long worshipped is debated.

A caution about 'Mithras'

The Roman mystery cult of Mithras, popular among soldiers in the first four centuries CE, took the Iranian god's name and an 'eastern' colouring but was a distinct Western creation with its own myth of the bull-slaying; it should not be read back as straightforward evidence for Achaemenid Mithra. Herodotus, for his part, garbles the god at 1.131, wrongly making 'Mitra' a goddess of love — a reminder of how Persian religion reached the Greeks at second hand.