Histories
Herodotus
Herodotus. Godley, Alfred Denis, translator. Cambridge, MA; London: Harvard University Press; William Heinemann, Ltd., 1920-1925 (printing).
Three sons had been born to Darius before he became king by his first wife, the daughter of Gobryas, and four more after he became king by Atossa daughter of Cyrus. Artobazanes was the oldest of the earlier sons, Xerxes of the later;
and as sons of different mothers they were rivals. Artobazanes pleaded that he was the oldest of all Darius' offspring and that it was everywhere customary that the eldest should rule; Xerxes argued that he was the son of Cyrus' daughter Atossa and that it was Cyrus who had won the Persians their freedom.
While Darius delayed making his decision, it chanced that at this time Demaratus son of Ariston had come up to Shush [48.333,32.2] (inhabited place), Khuzestan, Iran, AsiaSusa, in voluntary exile from Lacedaemonia after he had lost the kingship of Sparta [22.4417,37.0667] (Perseus) Sparta.