History of the Peloponnesian War

But when the thirty ships of the Athenians reached the coast of Thrace, they found Potidaea and the other places already in revolt.

Whereupon the generals, thinking it impossible with their present force to wage war with both Perdiccas and the places which had revolted, turned their attention to Macedonia, which was their destination at the start, and when they had got a foothold carried on war in concert with Philip and the brothers of Derdas, who had already invaded Macedonia from the interior with an army.

Thereupon the Corinthians, seeing that Potidaea had revolted and the Attic ships were in the neighbourhood of Macedonia, were alarmed about the place and thinking that the danger came home to them, dispatched volunteers of their own and such other Peloponnesians as they induced by pay, in all sixteen hundred hoplites and four hundred light-armed troops. The general in command was Aristeus son of Adimantus;

and it was chiefly because of friendship for him that most of the soldiers from Corinth went along as volunteers; for he had always been on friendly terms with the Potidaeans.

And they arrived on the coast of Thrace on the fortieth day after the revolt of Potidaea.