The naval Battle of Cyzicus took place in 410 BC during the Peloponnesian War. In the battle, an Athenian fleet commanded by Alcibiades, Thrasybulus, and Theramenes routed and completely destroyed a Spartan fleet commanded by Mindarus. The victory allowed Athens to recover control over a number of cities in the Hellespont over the next year. In the wake of their defeat, the Spartans made a peace offer, which the Athenians rejected.
In the wake of the Athenian victory at Abydos
in November 411 BC
, the Spartan admiral Mindarus sent to Sparta for reinforcements and began working with the Persian
to plan for a new offensive. The Athenians, meanwhile, were unable to follow through on their victory, since the depletion of the Athenian treasury precluded any major operations 
. Thus, by the spring of 410 BC, Mindarus had built a fleet of eighty ships, and with the support of Pharnabazus’s troops, besieged and took the city of Cyzicus
. The Athenian fleet in the Hellespont withdrew from its base at Sestos
to avoid the superior Spartan force, and ships under Alcibiades, Theramenes, Thrasybulus that had been dispatched to raise money combined with this force, creating a fleet of 86 ships 
. This fleet, along with a force of land troops under Chaereas
, set out to the Hellespont to challenge Mindarus.
2. The battle
The Athenian force entered the Hellespont, and, passing the Spartan base at Abydos by night so as to conceal their numbers, established a base on the island of Proconnesus
), just northwest of Cyzicus. The next day, they disembarked Chaereas’s force near Cyzicus. The Athenian fleet then divided, with 20 ships under Alcibiades advancing towards Cyzicus while two other divisions under Thrasybulus and Theramenes lurked behind. Mindarus, seeing an opportunity to attack what appeared to be a vastly inferior force, set out towards them with his entire force. Alcibiades’s force fled, and Mindarus’s ships gave chase. When both forces had gotten well out from the harbor, however, Alcibiades turned to face Mindarus, and Thrasybulus and Theramenes appeared with their forces to cut off his retreat. Mindarus, seeing the trap, fled in the one open direction, towards a beach south of the city, where Pharnabazus was located with his troops. The Spartan fleet suffered losses in the flight, and reached the shore with the Athenians right behind them.
Athenian naval strategy at the battle of Cyzicus: Alcibiades’ decoy force draws the Spartan fleet out into open water, and then turns about to engage them. Squadrons commanded by Thrasybulus and Theramenes move in behind the Spartan ships, to cut off their line of retreat, trapping the Spartans between three groups of Athenian warships; a much larger force than they had initially expected to engage.
Alcibiades’s troops, leading the Athenian pursuit, landed and attempted to pull the Spartan ships back out to sea with grappling hooks. The Persian troops under Pharnabazus, however, entered the fighting on the shore and began to drive the Athenians, who were outnumbered and fighting against opponents on firmer ground, into the sea. Seeing this, Thrasybulus landed his force as a diversion and ordered Theramenes to combine his troops with those of Chaereas and join the battle. For a time, Thrasybulus and Alcibiades were both driven back by superior forces, but the arrival of Theramenes and Chaereas turned the tide; the Spartans and Persians were defeated, Mindarus was killed. All the Spartan ships were captured save for those of the Syracusan
allies, who burned their ships as they retreated.
In the wake of this dramatic victory, the Athenians had full control of the waters of the Hellespont. The next day, they took Cyzicus, which surrendered without a fight. An intercepted letter from the Spartan troops stranded near Cyzicus reads “The ships are gone. Mindarus is dead. The men are starving. We know not what to do.”  Demoralized by the devastation of their fleet, the Spartans sent an embassy to Athens seeking to make peace; the Athenians rejected it  .
At Athens, the oligarchic government that had ruled since 411 gave way to a restored democracy within a few months of the battle. An expeditionary force under Thrasyllus
was prepared to join the forces in the Hellespont. This force, however, did not depart until over a year after the battle, and although the Athenians eventually recaptured Byzantium
and resumed collecting tribute from Chalcedon
, they never truly pressed the advantage that Cyzicus had given them. Largely, this was a result of financial inability; even after the victory, the Athenian treasury was hard pressed to support large-scale offensive operations 
. Meanwhile, the Spartans, with Persian funding, quickly rebuilt their fleet, and would go on to undermine the Athenian advantage. Athens would win only one more naval battle in the war, at Arginusae
, and their defeat at Aegospotami
in 405 BC
would bring the war to a close. Cyzicus, although a dramatic victory, failed to bring any lasting advantage to the Athenian side, and only served to postpone the eventual outcome of the war.