History of the Peloponnesian War
Thucydides
Thucydides. The history of the Peloponnesian War, Volume 1-2. Dale, Henry, translator. London: Heinemann and Henry G. Bohn, 1851-1852.
When the winter was closing, and spring was now at hand, the Argives went with scaling ladders to Epidaurus, supposing that it would be left unguarded on account of the war, and intending to take it by storm; but returned unsuccessful. And thus the winter ended, and the thirteenth year of this war.
In the middle of the next summer, when the Lacedaemonians saw that the Epidaurians, who were their allieswere in distress, and that the other states in the Peloponnese had either separated from them, or were unfavourably disposed towards them; thinking that if they did not quickly prevent it, they would proceed to a greater degree of disaffection, they marched with all their forces, themselves and the helots, against Argos, under the command of Agis son of Archidamus, king of the Lacedaemonians.
They were accompanied by the Tegeans, and as many others of the Arcadians as were in alliance with them. The allies in the rest of the Peloponnese also, and those beyond it, mustered at Phlius; the Boeotians with five thousand heavy-armed, the same number of light-armed, five hundred cavalry, and an equal number of [*]( i. e. light infantry who accompanied the cavalry into action See Poppo's note.) hamippi; the Corinthians with two thousand heavy-armed; the rest as might severally happen; but the Phliasians in full force, as the army was posted in their country.
Now the Argives had from the first been aware of the preparations of the Lacedaemonians; and when they were on their march for the purpose of joining the rest at Phlius, then they also took the field. They were reinforced by the Mantineans with their allies, and by three thousand heavy-armed of the Eleans.
And as they advanced, they met the Lacedaemonians at Methydrium in Arcadia, and each army occupied a hill. The Argives then prepared to engage the Lacedaemonians, cut off as they were by themselves: but Agis broke up in the night, and eluding them, proceeded to the rest of the allies at Phlius.