The unsuccessful siege of Miletus (412 BC) was a major Athenian setback early in the Ionian phase of the Great Peloponnesian War, and helped establish a revolt against Athenian power in the area.
In the aftermath of the major Athenian disaster at Syracuse, the Spartans decided to try and encourage revolts across the Athenian maritime empire. They also entered into negotiations with the nearest Persian satraps, and in particular with Tissaphernes, who controlled the western part of Asia Minor. This had once included the Greek cities of the Ionian coast, but they had been freed by an Athenian led alliance after the Persian Wars, and most of the cities became part of the Athenian Empire.
The situation was further complicated by the presence of Alcibiades, an Athenian leader who had been exiled early in the campaign on Sicily, and who after a period in Sparta had moved east into Persian territory, where he was now on good terms with Tissaphernes.
The first major revolt broke out on Chios. Both sides now prepared to send major fleets to the area, while smaller forces were rushed out. The Spartans managed to get a small fleet under Chalcideus into the area, while the Athenians sent squadrons under Strombichides and Thrasicles.
Alcibiades had good contacts in Miletus, and he wanted to convince them to join the revolt before the major Peloponnesian fleet could arrive and its commanders take the credit. He and Chalcideus raised a fleet of twenty ships, and pursued by nineteen ships under the Athenian commanders, reached Miletus just ahead of them. As Alcibiades had expected the city quickly agreed to revolt, and the Athenians were forced to retreat to the nearby island of Lade, from where they blockaded the city.
Soon after the start of the revolt in Miletus, the first formal alliance between the Persians and Sparta was agreed. Tissaphernes then spent some time campaigning along the coast, but he returned in time to take part in the larger battle to take place outside the city.
For the moment the Athenians had the upper hand, although the siege was more of a blockade. During the summer they landed at Panormus, south of the city, and in a minor battle killed the Spartan commander Chalcideus.
Late in the summer the two main fleets drew close. The Athenians arrived first, and landed close to Miletus with 3,500 men. A mixed army from Miletus, Persian and the Peloponnese came out to face them, with both Alcibiades and Tissphernes fighting with it. The resulting battle of Miletus was an Athenian victory, but on the evening after the battle news reached them that a larger Peloponnesian fleet had arrived in the area. Most of the army wanted to fight, but Phrynichus, one of the three generals, refused to risk losing Athens's last major army, and refused to flight. The Athenian fleet retreated to Samos, and the Peloponnesians were able to sail into Miletus, lifting the siege. After this the city became the main Peloponnesian base in Ionia.