The battle of Alyzeia (June or July 375 BC) saw the Athenians defeat a Spartan fleet that was supporting an attempt to move troops across the Corinthian Gulf into Boeotia (Theban-Spartan or Boeotian War, 379-371 BC).
In 379, 378 and 377 the Spartans had reached Boeotia by land, although their campaigns hadn't achieved much. In 376 King Cleombrotus hadn’t even got as far as Boeotia, and had abandoned the entire campaign after suffering a minor defeat while attempting to cross the Cithaeron mountain range. This Spartan failure gave the Thebans a chance to conquer their remaining strongholds in Boeotia, and by the spring of 375 only Plataea in the south and Orchomenus in the north-west remained in Spartan hands. Even their former base at Thespiae had been lost.
In 375 the Spartans decided to ship an army across the Corinthian Gulf into Boeotia, in an attempt to bypass the difficult land route. Thebes asked for help from Athens, now the head of a Second Athenian League. The Athenians raised a fleet of sixty ships, and gave command to Timotheus, the son of the famous Athenian admiral Conon. Timotheus led his fleet around the Peloponnese, raiding the coast as he went. On his arrival in the west he was able to win over Corcyra (modern Corfu), Cephalonia, and some of the cities of Acarnania, on the northern shores of the Corinthian Gulf.
The Spartans responded to the Athenian presence by sending a fleet of 55 ships into the Gulf, under the command of Nicolochus. The Spartans found the Athenian fleet at Alyzeia, on the coast of Acarnania, just outside the Corinthian Gulf. Nearby was the island of Kalamos, with another smaller island further to the south. Timotheus decided to try and take advantage of the difficult waters and the local knowledge of some of his ship's crews. Most of his fleet was beached, and the crews were rested. His fastest ships were sent out to harass the Spartans, avoiding getting too close to the enemy and tiring them out. The Spartans made a serious of unsuccessful attempts to get to grips with these ships, and in the process wore themselves out. After several hours the rest of the Athenian fleet put to sea, and won a significant victory.
It is possible that Spartan reinforcements, sent from Sicily and Ambracia, arrived just after this battle, and found the Athenian fleet disorganised after the battle. Timotheus was hampered by a number of captured ships, but he managed to form part of his fleet into a cresent, with the prows pointing towards the enemy, and then back-watered to the safety of the shore.
In the aftermath of the battle the Athenians erected a victory trophy. Soon afterwards Nicolochus probably returned to the scene with reinforcements, and erected a trophy of his own after Timotheus refused to fight. This was followed by the news that peace had been agreed between Athens, Sparta and Thebes, officially bringing the naval campaign to an end. Elsewhere the peace held for a couple of years, but in the west it was very quickly breached. On the Athenian side Timotheus helped restore the democratic faction on Zacynthus, while the Spartans attempted to intervene in the politics of Corcyra, acting in support of a group of exiled oligarchs. In 373 this turned into a full scale intervention, which ended with another Spartan defeat (siege and battle of Corcyra, 373-372 BC).