History of the Peloponnesian War

The same summer Hagnon, son of Nicias, and Cleopompus, son of Clinias, the colleagues of Pericles, took the armament of which he had lately made use, and went off upon an expedition against the Chalcidians in the direction of Thrace and Potidaea, which was still under siege. As soon as they arrived, they brought up their engines against Potidaea and tried every means of taking it,

but did not succeed either in capturing the city or in doing anything else worthy of their preparations. For the plague attacked them here also, and committed such havoc as to cripple them completely, even the previously healthy soldiers of the former expedition catching the infection from Hagnon's troops; while Phormio and the sixteen hundred men whom he commanded only escaped by being no longer in the neighborhood of the Chalcidians.

The end of it was that Hagnon returned with his ships to Athens, having lost one thousand and fifty out of four thousand heavy infantry in about forty days; though the soldiers stationed there before remained in the country and carried on the siege of Potidaea.