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.