The ravages of the pestilence continued in Attica for two years without any abatement; and in the fourth summer of the war, 428, the country was again invaded by a Peloponnesian army under the command of king Archidamus. The policy which prudence had dictated to Pericles was maintained after his death, partly perhaps through the weakness and depression caused by the sickness, and partly because the enemy's presence had now become more familiar, and no longer excited the same emotions. The Athenians contented themselves with annoying the enemy, as opportunity offered itself, with their cavalry, which prevented his light troops from spreading over the country, and infesting the immediate neighbourhood of the city, and forced them to keep within the shelter of the heavy infantry. At the same time they equipped a fleet of forty galleys, which prepared to sail round Peloponnesus, under the command of Cleippides and two colleagues.

But in the mean while they were threatened in a distant quarter with a blow, which, if it had taken effect, not only would have immediately weakened their power, but might have proved ruinous in its remote consequences. We have already mentioned, that before the war broke out Mitylene had only been prevented from casting off the Athenian yoke by the reluctance which the Spartans felt to break the Thirty Years' Truce.