History of the Peloponnesian War

In this way Brasidas stole a rapid march through Thessaly, before any one was prepared to stop him, and reached Perdiccas and Chalcidice.

For what brought the army up out of the Peloponnese, while the affairs of Athens were so prosperous, was the fear of the Thrace-ward cities which had revolted from the Athenians, and that of Perdiccas:

the Chalcidians thinking that the Athenians would in the first place march against them, (and moreover, the cities near to them which had not revolted, secretly joined in the invitation,) and Perdiccas, though not an open enemy, yet being afraid, on his part also, because of his old quarrels with the Athenians, and most of all being desirous of reducing to subjection Arrhibaeus, the king of the Lyncestians.

And what contributed to their getting the army out of the Peloponnese the more easily, was the misfortune of the Lacedaemonians at that time. For as the Athenians were pressing hard upon the Peloponnese, and especially upon their territory, they hoped to divert them from it most effectually, if they annoyed them in return by sending an army to their allies; especially as they were ready to maintain it, and were calling them to their aid, with a view to revolting.

Besides, they were glad to have a pretext for sending away some of the Helots; lest in the present state of affairs, when Pylus was occupied by an enemy, they might attempt some revolution.

Indeed through fear of their youth and great numbers, they even perpetrated the following deed: (for at all times most of the Lacedaemonian institutions were framed particularly with a view to the Helots, to guard against them.) They made proclamation, that as many of them as claimed to have done the state most service against the enemy should be picked out, professing that they would give them their liberty; thus applying a test to them, and thinking that those who severally claimed to be first made free, would also, through their high spirit, be most ready to attack them.