The siege of Delphinium (406 BC) was a minor Peloponnesian success that came early in the command of Callicratidas, an admiral who replaced the popular Lysander in command of the Peloponnesian fleet in Asia Minor (Great Peloponnesian War).
Callicratidas took control of a fleet of 140 warships, including 50 newly provided by Sparta's allies, as well as the fleet recently commanded by Lysander.
Callicratidas' first target was the Athenian held fortress of Delphinium, on Chios. Chios had been one of the first areas to rebel against Athenian control after the disaster on Syracuse, and the Athenians had since been unable to regain control of the island, but they had managed to blockade it for some time.
Delphinium was defended by a garrison of 500 Athenians, far too small to successfully defend the fortress against the entire Peloponnesian fleet. The defenders soon realised this, and arranged to surrender the fortress on terms. The garrison was allowed to march through the Peloponnesian lines and join other Athenian forces. The fortress was levelled to the ground. Callicratidas then moved on to attack Methymne on Lesbos, before clashing with the main Athenian fleet under Conon and blockading them in Mitylene.