The most southern part of the plain of Argos has at all times had a great abundance of water, but with little or no profit to agriculture; for the sea-shore is lined with vast and almost impassable swamps, and the river Erasinus, which pours down from Mount Chaon, soon empties itself into the Gulf of Nauplia. Further, the springs at the foot of Mount Pontinus form the famous swamps of Lerna, where Hercules is fabled to have killed the Hydra. Probably this myth is the symbolic account of an attempt once made to drain the swamps and to convert them into arable land. Owing to its exuberant fertility and exceptional situation on the splendid gulf, this plain has been the natural centre and the point of departure for the whole political and social development of the country, and for this reason it deserves the appellation "ancient Argos."[102] Here Phoroneus, son of the river Inachus and the nymph Meleia, was said, with his wife Niobe, to have first united the inhabitants, who till then had lived dispersed, into one community, and to have founded a city which he called ῎Αστυ ϕορωνικόν,[103] which was renamed by his grandson Argos, and became the centre of a powerful Pelasgic state.[104] Indisputable proofs of this Pelasgic settlement are found in both the names Argos and Larissa, which are Pelasgic, the former meaning "plain," the latter "fortress"; further, in the myth of the ancient Pelasgic moon and cow-goddess Iö, who, as has been said above, was fabled to have been born here, her father being the river Inachus. The Pelasgic state comes afterwards under the dominion of the Pelopids, under whom the country is divided into two states, as we find it still in the Iliad; the northern part, with the capital Mycenæ, being under the sceptre of Agamemnon; the southern, with Argos as its capital, under the dominion of Diomedes, who was, however, only a vassal of the former. At all events, at the time of the invasion of the Peloponnesus by the Dorians, Argos was the mightiest state in the peninsula, and thus tradition allots it to the Heraclid Temenus, the firstborn son of Aristomachus. [Sidenote: SITUATION OF MYCENÆ.]