In the summer of 336, Darius III Codomannus became king of Persia. This brave man was to be the last king of the ancient empire, because he was defeated by Alexander the Great.
Darius became king after a very troubled succession. The Greek author Diodorus of Sicily, describes the events in section 17.5.3-6.3 of his World history. The two kings, whom Diodorus calls Ochus and Arses, are better known as Artaxerxes III Ochus and Artaxerxes IV Arses.
The translation was made by C. Bradford Welles.
[17.5.3] While Philip was still king, Ochus ruled the Persians and oppressed his subjects cruelly and harshly. Since his savage disposition made him hated, the chiliarchnote Bagoas, a eunuch in physical fact but a militant rogue in disposition, killed him by poison administered by a certain physician. And he placed upon the throne the youngest of Ochus' sons, Arses.note
[17.5.4] He similarly made away with the brothers of the new king, who were barely of age, in order that the young man might be isolated and tractable to his control.
But the young king let it be known that he was offended at Bagoas' previous outrageous behavior and was prepared to punish the author of these crimes, so Bagoas anticipated his intentions and killed Arses and his children also, while he was still in the third year of his reign.
[17.5.5] The royal house was thus extinguished, and there was no one in the direct line of descent to claim the throne.
Instead, Bagoas selected a certain Darius, a member of the court circle, and secured the throne for him. He was the son of Arsames, and grandson of that Ostanes who was a brother of Artaxerxesnote, who had been king.
[17.5.6] As to Bagoas, an odd thing happened to him and one to point a moral. Pursuing his habitual savagery he attempted to remove Darius by poison. The plan leaked out, however, and the king, calling upon Bagoas, as it were, to drink to him a toast and handing him his own cup compelled him to take his own medicine.
[17.6.1] Darius' selection for the throne was based on his known bravery, in which quality he surpassed the other Persians. Once when king Artaxerxesnote was campaigning against the Cadusians, one of them with a wide reputation for strength and courage challenged a volunteer among the Persians to fight in single combat with him. No other dared accept, but Darius alone entered the contest and slew the challenger, being honored in consequence by the king with rich gifts, while among the Persians he was conceded the first place in prowess.
[17.6.2] It was because of this prowess that he was thought worthy to take over the kingship. This happened about the same time as Philip died and Alexander became king.
[17.6.3] Such was the man whom fate had selected to be the antagonist of Alexander's genius, and they opposed one another in many and great struggles for the supremacy.