Thucydides, History of the Peloponnesian War
Benjamin Jowett, Ed.

40. Meanwhile the Chians and Pedaritus continued to send messengers to Astyochus, who continued¹ to delay. They implored him to come to their help with his whole fleet, saying that they were blockaded, and that he should not allow the chief ally of Sparta in Ionia to be cut off from the sea and overrun and devastated by land. [2] Now the Chians had more domestic slaves than any other state with the exception of Lacedaemon, and their offences were always more severely punished because of their number; so that, when the Athenian army appeared to be firmly settled in their fortifications, most of them at once deserted to the enemy². And they did the greatest damage, because they knew the country. [3] The Chians pressed upon the Lacedaemonians the necessity of coming to their assistance while there was still hope of interfering to some purpose; the fortification of Delphinium, though not yet completed, was in progress, and the Athenians were beginning to extend the lines of defence which protected their army and ships. Astyochus, seeing that the allies were zealous in the cause, although he had fully meant to carry out his threat, now determined to relieve the Chians.