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

58. The Argives, having had previous notice of the Lacedaemonian preparations, and seeing that¹ they were actually on their march to join the rest of the army at Phlius, now took the field themselves. The Mantineans and their allies and three thousand Elean hoplites came to their aid. [2] They advanced to the territory of Methydrium in Arcadia, where they fell in with the Lacedaemonians. The two armies each occupied a hill, and the Argives, thinking that they now had the Lacedaemonians alone, prepared for action. But in the night Agis removed his forces unknown to them and went to join the allies at Phlius. [3] At dawn the Argives became aware of his departure, and moved first towards Argos, then to the Nemean road, by which they expected the Lacedaemonians and their allies to descend into the plain. [4] But Agis, instead of taking the road by which he was expected, led the Lacedaemonians, Arcadians, and Epidaurians by a more difficult path, and so made his way down; the Corinthians, Pellenians, and Phliasians went by another steep pass; the Boeotians, Megarians, and Sicyonians he commanded to descend by the Nemean road, where the Argives had taken up their position, in order that, if the Argives should return and attack his own division of the army in the plain, they might be pursued and harassed by their cavalry. [5] Having made these dispositions, and having come down into the plain, he began to devastate Saminthus and the neighbourhood.