The main result of the Peloponnesian War was that the Persian Empire improved its position in Asia Minor. Several Greek cities that had for half a century been protected by the Delian League, became dependent upon the Great King. No Greek can have been surprised, because the Spartans had already tried to strike a deal with Persia at the beginning of the war. Their ambassadors, however, did not reach the Persian court.
The story is told by the Athenian historian Thucydides (History of the Peloponnesian War 2.67; translated by Rex Warner), and was well-known. It is also the latest event told by Herodotus of Halicarnassus.
Aneristus and Nicolaus
[2.67.1] At the end of the summernote[Of 430.] an embassy consisting Aristeus from Corinth, Aneristus, Nicolaus, and Stratodemus from Sparta, Timagoras from Tegea, and a man from Argos called Pollis, who was acting on his private initiative, was on its way to Asia with the object of persuading the King of Persia to provide money and join the war on the Spartan side.
[2.67.2] First however, they came to Sitalces,note[King of Thrace.] the son of Teres, in Thrace, wanting, if possible, to induce him to abandon his alliance with Athens and send an army to relieve Potidaea, which was still being besieged by the Athenian forces. They also wanted to have his help in getting across the Hellespont to their destination in Asia, where they were to meet Pharnaces, the son of Pharnabazus, who was going to send them on into the interior to the King.
[2.67.3] But it happened that there were some Athenian ambassadors with Sitalces: Learchus, the son of Callimachus, and Ameiniades, the son of Philemon. These two suggested to Sitalces' son Sadocus, who had just been made an Athenian citizen, that he should hand the men over to them, and not allow them to cross over to the King of Persia and try to injure the city which Sadocus had chosen for his own.
[2.67.4] Sadocus agreed, and as they were on their way through Thrace to the ship on which they were going to cross the Hellespont, he had them arrested by some troops which he had sent with Learchus and Ameiniades with instructions to hand over the men to the two Athenians.
[2.67.5] They, on receiving the prisoners, brought them to Athens and, as soon as they arrived there, the Athenians, fearing that Aristeus, who even before then appeared to have had the chief hand in all their troubles in Potidaea and in Thrace, might do them more harm still if he escaped, on that same day, without giving them a trial or allowing them to say what they wished to say in their defense, put them all to death and threw their bodies into a pit.
They regarded this action as legitimate retaliation for the way in which the Spartans had been behaving, since they also had killed and thrown into pits all Athenian and allied traders whom they had caught sailing in merchant ships around the Peloponnese. Indeed, at the beginning of the war the Spartans killed as enemies all whom they captured on the sea, whether allies of Athens or neutrals.