Plutarch, Nicias
Bernadotte Perrin, Ed.

After Demosthenes had fortified Pylos,¹ the Peloponnesians came up against it by land and sea, a battle was fought, and about four hundred Spartans were shut off on the island of Sphacteria. Then the Athenians considered that their capture would be a great achievement, as was true. But the siege was difficult and toilsome, since the region afforded little fresh water. Even in summer the shipping of the necessary supplies round Peloponnesus was a long and expensive process, while in winter it was sure to be perilous if not altogether impossible. The Athenians were therefore in bad humor, and repented them of having repulsed an embassy of the Lacedaemonians which had come to treat with them for a truce and peace. [2] They had repulsed it because Cleon, chiefly on account of Nicias, was opposed to it. For he hated Nicias, and when he saw him zealously cooperating with the Lacedaemonians, persuaded the people to reject the truce. So when the siege grew longer and longer, and they leaned that their forces were in terrible straits, they were angry with Cleon. [3]

He, however, laid all the blame on Nicias, and denounced him, saying that it was through cowardice and weakness that he was letting the men on the island slip through his hands, whereas, had he himself been general instead of Nicias, they would not have held out so long. Thereupon it occurred to the Athenians to say: ‘It's not too late! Why don't you sail yourself and fetch the men?’ Nicias too rose in the assembly and resigned his command of the expedition to Pylos in favour of Cleon, bidding him take as large a force as he wished, and not to vent his boldness in mere words which brought no peril with them, but to perform some deed for the city which would be worth its notice. [4] At first Cleon tried to draw back, confused by the unexpectedness of this offer; but the Athenians kept up the same cries of encouragement, and Nicias kept taunting him, until, his ambition incited and on fire, he undertook the command, and, besides, declared in so many words that within twenty days after sailing he would either slay the men on the island or bring them alive to Athens. The Athenians were moved to hearty laughter at this rather than to belief in it, for they were already in the way of treating his mad vanity as a joke, and a pleasant one too. [5]

It is said, for instance, that once when the assembly was in session, the people sat out on the Pnyx a long while waiting for him to address them, and that late in the day he came in all garlanded for dinner and asked them to adjourn the assembly to the morrow. ‘I'm busy to-day,’ he said, ‘I'm going to entertain some guests, and have already sacrificed to the gods.’ The Athenians burst out laughing, then rose up and dissolved the assembly.