History of the Peloponnesian War

When the Syracusans and allies were assembled together, they took with them as many prisoners as they could, with the spoils, and returned to the city.

All the rest of the Athenians and the allies that they had taken, they sent down into the quarries, thinking this the safest way of keeping them: but Nicias and Demosthenes they executed, against the wish of Gylippus. For he thought it would be a glorious distinction for him, in addition to all his other achievements, to take to the Lacedaemonians even the generals who had commanded against them.

And it so happened, that one of these, namely Demosthenes, was regarded by them as their most inveterate enemy, in consequence of what had occurred on the island and at Pylus; the other, for the same reasons, as most in their interest; for Nicias had exerted himself for the release of the Lacedaemonians taken from the island, by persuading the Athenians to make a treaty.

On this account the Lacedaemonians had friendly feelings towards him; and indeed it was mainly for the same reasons that he reposed confidence in Gylippus, and surrendered himself to him. But certain of the Syracusans (as it was said) were afraid, some of them, since they had held communication with him, that if put to the torture, he might cause them trouble on that account in the midst of their success; others, and especially the Corinthians, lest he might bribe some, as he was rich, and effect his escape, and so they should again incur mischief through his agency;

and therefore they persuaded the allies, and put him to death. For this cause then, or something very like this, he was executed; having least of all the Greeks in my time deserved to meet with such a misfortune, on account of his devoted attention to the practice of every virtue.