Thucydides, History of the Peloponnesian War
Benjamin Jowett, Ed.

68. About the end of the same summer the Ambraciots, with a large Barbarian force which¹ they had called out, made war upon the Amphilochian Argos and upon Amphilochia. [2] The original cause of their enmity against the Argives was as follows:— [3] The Amphilochian territory had been occupied and the city founded by Amphilochus the son of Amphiaraus, who on returning home after the Trojan War was dissatisfied at the state of Argos. He fixed the site on the shore of the Ambracian Gulf, and called the new city by the name of his native place; [4] it was the greatest city in that region, and its inhabitants were the most powerful community. [5] Many generations afterwards, these Amphilochians in a time of distress invited their neighbours the Ambraciots to join in the settlement, and from them they first learned the Hellenic language which they now speak; [6] the other Amphilochians are Barbarians. After a while the Ambraciots drove out the Amphilochian Argives and themselves took possession of the city. [7] The expelled Amphilochians placed themselves under the protection of the Acarnanians, and both together called in the Athenians, who sent them a fleet of thirty ships under the command of Phormio. When Phormio arrived, they stormed Argos, and sold the Ambraciots into slavery; [8] and the Amphilochians and Acarnanians dwelt together in the place. The alliance between the Acarnanians and Athenians then first began. [9] The hatred of the Ambraciots towards the Amphilochian Argives commenced with the enslavement of their countrymen; and now when the war offered an opportunity they invaded their territory, accompanied by the Chaonians and some others of the neighboring Barbarians. They came as far as Argos and made themselves masters of the country; but not being able to take the city by assault they returned, and the several tribes dispersed to their own homes. Such were the events of the summer.