History of the Peloponnesian War

Perdiccas at the same time per suaded the Chalcidians to abandon and pull dowr their cities on the sea-coast and settle inland at Olynthus, making there a single strong city; and he gave them, when they abandoned their cities, a part of his own territory of Mygdonia around Lake Bolbe to cultivate as long as they should be at war with the Athenians. And so they proceeded to dismantle their cities, move inland, and prepare for 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.