History of the Peloponnesian War

The Lacedaemonians, when they found the war against those in Ithome prolonged, called other allies to their aid, and the Athenians also; who went under the command of Cimon with no small force.

They asked their aid, because they were considered to be skilful in conducting sieges: whereas in themselves, from the siege having been so protracted, there seemed to be a deficiency of this skill; for else they would have taken the place by assault.

It was from this expedition that the first open quarrel arose between the Lacedaemonians and Athenians. For the Lacedaemonians, when the place was not taken by storm, fearing the boldness and innovating spirit of the Athenians—and moreover considering that they were of a different race from themselves—lest, if they remained, they might at the persuasion of those in Ithome attempt some revolution, dismissed them alone of all the allies; not letting their suspicion appear, but saying that they were no longer in any need of them.

The Athenians, however, knew that they were dismissed, not on the more creditable reason assigned, but from some suspicion having arisen: and considering it hard usage, and not thinking that they deserved to be so treated by the Lacedaemonians, immediately on their return they broke off the alliance which they had made with them against the Mede, and became allies of the Argives, their enemies. The same oaths also were taken, and the same alliance made by both with the Thessalians.