The Battle of Aegospotami was a naval confrontation that took place in 405 BC and was the last major battle of the Peloponnesian War. In the battle, a Spartan fleet under Lysander destroyed the Athenian navy. This effectively ended the war, since Athens could not import grain or communicate with its empire without control of the sea.
In 405 BC, following the severe Spartan defeat at the Battle of Arginusae, Lysander, the commander who had been responsible for the first Spartan naval successes, was reinstated in command. Since the Spartan constitution prohibited any commander from holding the office of navarch more than once, he was appointed as a vice-admiral instead, with the clear understanding that this was a mere legal fiction.
One of Lysander's advantages as a commander was his close relationship with the Persian prince Cyrus. Using this connection, he quickly raised the money to begin rebuilding the Spartan fleet. When Cyrus was recalled to Susa by his father Darius, he gave Lysander the revenues from all of his cities of Asia Minor. With the resources of this entire wealthy Persian province at his disposal, Lysander was able to quickly reconstitute his fleet.
He then set off on a series of campaigns throughout the Aegean. He seized several Athenian-held cities, and attacked numerous islands. He was unable to move north to the Hellespont, however, because of the threat from the Athenian fleet at Samos. To divert the Athenians, Lysander struck westward. Approaching quite near to Athens itself, he attacked Aegina and Salamis, and even landed in Attica. The Athenian fleet set out in pursuit, but Lysander sailed around them, reached the Hellespont, and established a base at Abydos. From there, he seized the strategically important town of Lampsacus, opening the way to the Bosporus. Should he reach the strait, he could close down the trade routes from which Athens received the majority of her grain. If the Athenians were to avoid starvation, Lysander had to be contained immediately.