Evidence of his wealth is found in the fact that he had no fewer than 1000 slaves whom he hired out. He gravitated naturally to the aristocratic party, and was several times colleague with Pericles in the strategia. On the death of Pericles he was left leader of the aristocrats against the advanced party of Cleon. He made use of his wealth both to buy off enemies (especially informers) and to acquire popularity by the magnificent way in which he discharged various public services, especially those connected with the state religion, of which he was a strong supporter. In the field he displayed extreme caution, and prior to the great Sicilian expedition achieved a number of minor military successes. Plutarch states that "Nicias declined all difficult and lengthy enterprises; if he took a command, he was for doing what was safe."
In 421 he took a prominent part in the arrangement of the "Peace of Nicias," which terminated the first decade of the Peloponnesian War. He now entered with varying success upon a period of rivalry with Alcibiades, the details of which are largely matters of conjecture. So bitter was the strife that the ostracism of one seemed inevitable, but by a temporary coalition they secured instead the banishment of the demagogue Hyperbolus (417). In 415 he was appointed with Alcibiades and Lamachus to command the Sicilian expedition, and, after the flight of Alcibiades and the death of Lamachus, was practically the sole commander, the much more capable Demosthenes (not the orator), who was sent to his aid, being apparently of comparatively little weight.
The expedition turned out to be a disaster and Nikias himself was captured and taken prisoner. He was executed despite orders to the contrary by Spartan commander Gylippus. His surviving troops were made slaves to work in the quarries of Sicily.
How far it is just to attribute to his excessive caution and his blind faith in omens the disastrous failure it is difficult to say. At all events it is clear that the management of so great an enterprise was a task far beyond his powers. He was a man of conventional respectability and mechanical piety, without the originality which was required to meet the crisis which faced him. His popularity with the aristocratic party in Athens is, however, strikingly shown by the lament of Thucydides over his death: "He assuredly, among all Greeks of my time, least deserved to come to so extreme a pitch of ill-fortune, considering his exact performance of established duties to the divinity" (vii. 86, Crete's version).
- Plutarch's Parallel Lives