These preparations were interrupted by the Athenian fleet, which had been notified of the plot, and the Mytileneans sent representatives to Athens to discuss a settlement, but simultaneously dispatched a secret embassy to Sparta to request support.
Although Sparta finally dispatched a fleet in the summer of 427 BC, it advanced with such caution and so many delays that it arrived in the vicinity of Lesbos only in time to receive news of Mytilene's surrender.
Before they had completed their preparations, however, their plans were betrayed to the Athenians by several of their enemies in the region, namely the Methymnians and Tenedians, and by a group of Mytilenean citizens who represented Athens' interests in that city (probably members of the democratic faction there).
[4] The Athenians, who were still suffering from the plague at this time and were under great financial strain from the unexpectedly long and involved war, initially tried to negotiate in order to avoid taking on yet another military commitment in Lesbos.
[8] The Mytileneans mustered an army and marched out to attack the Athenian camp; although they came off slightly the better in the ensuing battle, they were unwilling to press their advantage and retreated back behind their fortifications before nightfall.
At this point the Athenians, encouraged by the lack of initiative on their enemies' part, summoned troops from their allies and, once these arrived, built two fortified camps, one on either side of Mytilene's harbor.
[9] This second group of Mytilenean ambassadors arrived within a week of the first, in July, but neither secured any immediate assistance; the Spartans deferred the decision over Mytilene to the Peloponnesian League as a whole, which would be convening at Olympia later that summer.
[14] The Athenians, meanwhile, aware that the Peloponnesian's readiness to attack derived in part from the Mytileneans' assertions that Athens was critically weakened, prepared a fleet of 100 ships to raid the coast of the Peloponnese.
[20] In the summer of 427 BC, the Spartans and their allies planned a concerted effort on land and sea to strain Athens' resources and relieve the siege at Mytilene.
A Spartan representative, Salaethus, had been smuggled into the city in a trireme at the end of the winter with news of the relief scheme, and had taken command of the defenses there in anticipation of the fleet's arrival.
Realizing that they could not prevent this, and that a peace concluded without their involvement would surely be fatal to them, the members of the government contacted the Athenian commander and surrendered, on the condition that none of the Mytileneans should be imprisoned, enslaved, or executed until representatives from the city had presented their case at Athens.
Indeed, once he learned of Mytilene's surrender Alcidas's primary goal was to return home without having to confront the Athenian fleet, and he accordingly began sailing southwards down the Ionian coast.
[26] After he completed subduing Mytilene, Paches sent the greater part of his army back to Athens, and sent with it the Mytileneans whom he had identified as particularly culpable in the revolt and the captured Spartan general Salaethus.
On the first day, the events of which Thucydides only summarizes, the Athenians angrily condemned the entire male population of Mytilene to death, and the women and children to slavery.
[30] Aware of this trend, the Mytilenean delegation that had been sent to Athens to present that city's case asked the prytanies to call a meeting of the assembly, and those officials acquiesced.
This speech marks Cleon's first appearance in the historical record, and Thucydides introduces him by saying that "he was remarkable among the Athenians for the violence of his character, and at this time he exercised far the greatest influence over the people."
In Cleon's speech, as reported by Thucydides, the politician argues that consistent enforcement of laws, even when they seem unjust, is the only way to maintaining order, and moreover that the Mytilenean people as a whole (not merely the aristocracy) had revolted against Athens, and thus deserved to be condemned.
[38] The early portion of Diodotus' speech is devoted to refuting the charges that Cleon had preemptively levelled against those who would speak after him, principally by arguing that the assembly would deprive itself of wise counsel if it constantly examined the motives of speakers instead of the arguments they presented.
Throughout the speech, Diodotus refuses to stray from the grounds of expediency, reminding the Athenians that they sit not as a court of law but as political assembly, dedicated to determining what action is most advantageous for Athens.
In the famous passage where he lays out his methodology for reporting the content of speeches, Thucydides states that "my habit has been to make the speakers say what was in my opinion demanded of them by the various occasions, of course adhering as closely as possible to the general sense of what they really said.
Croix accepted Diodotus' statement as factual, and took the Mytilenean demos's threat to hand over the city as evidence that they had harbored secret pro-Athenian feelings throughout the siege.
[45] Both Donald Kagan and Ronald Legon, meanwhile, have emphasized that, whatever the feelings of the Mytilenean demos were, the people had clearly not displayed enough revolutionary sentiment to prevent their rulers from distributing arms to them.
For the Athenians, this solution solved several problems; the garrison would provide security on Lesbos, and the absence of its members from Athens would to an extent ease the overpopulation of that city and the strain on the treasury resulting from the need to feed thousands of displaced farmers.
[51] Donald Kagan has interpreted this anecdote to indicate that Paches, a moderate, was being prosecuted by Cleon or another more aggressive politician, who disapproved of his decision to break off the pursuit of Alcidas' fleet.