History of the Peloponnesian War

So many were the nations of Greeks and barbarians that inhabited Sicily, and such was the size of the island against which the Athenians were eager to make an expedition; being desirous (to mention their truest motive) of gaining dominion over the whole of it; but at the same time wishing, as a plausible pretext, to succour their own kinsmen, and the allies they had gained besides.

Above all, they were instigated by ambassadors from the Segestans, who had come to Athens and invoked their aid more earnestly than ever. For being borderers of the Selinuntines, they had gone to war with them on certain questions respecting marriage rights, and for some debated territory; and the Selinuntines, having taken the Syracusans for their allies, were pressing them hard with hostilities both by land and sea. Consequently the Segestans reminded the Athenians of their alliance, which had been formed in the time of Laches and of the former war with the Leontines, and begged them to send a fleet and assist them; alleging many other things, and, as the sum and substance of all,

that if the Syracusans should be unpunished for the depopulation of Leontini, and, by ruining such of the Athenian allies as were still left should themselves obtain the whole power of Sicily; there would be danger of their some time or other coming with a large force, as Dorians, to the aid of Dorians, on the strength of their connexion, and, moreover, as colonists, to the aid of the Peloponnesians who had sent them out, and so joining in the destruction of the Athenian power. It were wise therefore, in concert with the remaining allies, to resist the Syracusans;

especially as they would themselves furnish money sufficient for the war.