History of the Peloponnesian War

Then, having reached Mount Thyamus, which is uncultivated, they proceeded across it, and so came down into the Argive country by night, and passing unobserved between the city of Argos and the Acarnanian posts at Crenae, joined the Ambraciots at Olpae.

Having thus effected a union at day-break, they sat down at the place called Metropolis, and formed their encampment. Not long after, the Athenians came with their twenty ships into the Ambracian Gulf to assist the Argives; and Demosthenes arrived with two hundred heavy-armed of the Messenians, and sixty Athenian archers. The fleet therefore at Olpae blockaded the hill from the sea;

while the Acarnanians and a few of the Amphilochians (for the majority were forcibly detained by the Ambraciots) had by this time met at Argos, and were preparing to engage with the enemy, having appointed Demosthenes as commander of the whole army in concert with their own generals. He, having led them near to Olpae, encamped there;