History of the Peloponnesian War

And to me the imbecility of ancient times is not a little demonstrated also by this [that followeth]. For before the Trojan war nothing appeareth to have been done by Greece in common;

nor indeed was it, as I think, called all by that one name of Hellas; nor before the time of Hellen, the son of Deucalion, was there any such name at all. But Pelasgicum (which was the farthest extended) and the other parts, by regions, received their names from their own inhabitants. But Hellen and his sons being strong in Phthiotis and called in for their aid into other cities, these cities, because of their conversing with them, began more particularly to be called Hellenes; and yet could not that name of a long time after prevail upon them all. This is conjectured principally out of Homer.

For though born long after the Trojan war, yet he gives them not anywhere that name in general, nor indeed to any but those that with Achilles came out of Phthiotis and were the first so called; but in his poems he mentioneth Danaans, Argives, and Achaeans. Nor doth he likewise use the word barbarians; because the Grecians, as it seemeth unto me, were not yet distinguished by one common name of Hellenes, oppositely answerable unto them.