The date from which the following extract is taken is uncertain. Callisthenes was a Greek philosopher, the friend and advisor of Alexander the Great, who was put to death c. 330 BC. He was the author of a history of Greece and other works, none of which survive. The legendary story provided here was put together, probably in Egypt, in or about the end of the third century AD. Translations exist more or less complete in Syriac, Armenian, Ethiopic and others, besides a Latin rendering by Julius Valerius in the early part of the fourth century AD.
History of Greece I. 36:
I, Darius, king of kings and of the race of the gods, consort of Mithra on his throne and co-partner with the Sun, in my own right divine do give these injunctions and commands to thee my servant Alexander.
History of Greece I. 39:
Alexander the king, the son of king Philip and Olympias his mother, to the great king of the Persians, king of kings and consort of the Sun-god, off-spring o the gods and co-partner with the Sun, greeting. It is unworthy that Darius, so geat a king of the Persians, exalted with so great power, consort of the gods and co-partner with the Sun, should be reduced to mean servitude to a mere man Alexander.
History of Greece II. 14:
Alexander then seeing the great pomp of Darius was moved almost to worship him as Mithra the divine, as though clothed in barbaric splendor he had come down from heaven, - such was his splendid array. Darius was seated upon a lofty throne, with a crown of most precious stones, wearing a robe of Babylonian silk inwoven with golden thread.
[according to the Syriac version] And when Darius saw Alexander he did obeisance and worshipped Alexander, for he believed that he was Mihr [Mithras] the god, and that he had come down to bring aid to the Persians. For his raiment was like that of the gods, and the crown with rested upon his head shone with rays of light and the robe with he wore was woven with fine gold.
History of Greece III. 34:
The Persians contended with the Macedonians, wishing to carry off Alexander and to proclaim him as Mithras. But the Macedonians resisted, wishing to carry him back to Macedonia.