History of the Peloponnesian War (1.59.1-1.60.1)

The thirty ships of the Athenians arrived at the Thraceward towns, and found Potidaea and the rest in revolt:

and the generals thinking it impossible with their present force to carry on war both with Philip and the revolted towns, turned their attention to Macedonia, the object for which they were first sent out; and having established themselves there, [*] carried on the war in conjunction with Philip and the brothers of Derdas, who had invaded the country with an army from the interior.

And at this time, when Potidaea had revolted and the Athenian ships were cruising about Macedonia, the Corinthians, being alarmed for the place, and considering the danger to affect themselves, sent volunteers of their own people and mercenaries of the rest of the Peloponnesians, sixteen hundred heavy-armed in all and four hundred light-armed.