History of the Peloponnesian War

The reason why the peoples in Thrace who had revolted from Athens had, in conjunction with Perdiccas, brought this army all the way from the Peloponnesus was that they were filled with alarm at the success of the Athenians. The Chalcidians thought that the Athenians would take the field against them first, and the cities in this neighbourhood which had not yet revolted nevertheless took part secretly in inviting the Peloponnesians to intervene. As for Perdiccas, although he was not yet openly hostile to Athens, he also was afraid of the long-standing differences between himself and the Athenians, and above all he was anxious to reduce Arrhabaeus, the king of the Lyncestians.

A further circumstance which rendered it easier for them to procure an army from the Peloponnesus was the evil fortune which at the present time attended the Lacedaemonians.

For since the Athenians kept harassing the Peloponnesians, and especially the territory of the Lacedaemonians, the latter thought that the best way of diverting them would be to retaliate by sending an army against their allies, especially since these allies were ready to maintain an army and were calling upon the Lacedaemonians for help in order that they might revolt.

Furthermore, the Lacedaemonians were glad to have an excuse for sending out some of the Helots, in order to forestall their attempting a revolt at the present juncture when Pylos was in the possession of the enemy.