The Battle of Naupactus was a naval battle between the Athenian fleet under Phormio and a combined Spartan and Corinthian fleet. It took place over the course of a week in the early part of the Peloponnesian War in 429 BC.

The battle took place shortly after the Battle of Chalcis. Ambracia and Chaonia asked Sparta to send a fleet and an army to conquer Acarnania from Athens, which would allow Sparta to attack Naupactus, the Athenian naval base on the Gulf of Corinth. The Spartan general Cnemus, with a fleet and 1000 hoplites, ravaged Acarnania, while Phormio and the Athenian fleet waited in the Gulf of Corinth for the Corinthian fleet in case it tried to attack Naupactus. Cnedus was defeated at Stratus in Acarnania, while the Corinthian fleet was delayed in the Gulf by Phormio.

The Corinthians had 47 ships, commanded by Machaon, Isocrates, and Agatharchidas, and were not prepared to fight a battle against Phormio, even though he only had 20 ships, as they were attempting to bring aid and supplies to Cnedus. However, the Athenians followed them through the Gulf and would not let them leave. The larger Corinthian ships formed a circle to protect the support ships that were not armed for battle. The Athenians formed a line and continually sailed around the Corinthians, forcing the Corinthian circle to become compacted as they tried to avoid being rammed. The Corinthians were eventually unable to manoeuvre at all, and Phormio took this opportunity to attack. The Athenians captured 12 ships and sank many more, but allowed the rest to escape. The remnants of the Corinthian fleet then joined Cnedus in Acarnania.

Phormio continued to follow the Corinthians, which combined with the Spartan fleet, led by Timocrates, Brasidas, and Lycophron. Athens also sent out another 20 ships under Nicias, but this fleet was delayed near Crete. During the week after the first battle, the combined Peloponnesian fleet of 77 ships anchored at the entrance to the Gulf across from the Athenian ships. The Corinthians did not want another battle, and the Spartans felt they had been cowards in the first battle, so it was difficult to convince the Peloponnesian fleet to sail even though it greatly outnumbered the Athenian fleet. Cnemus and Brasidas tried to convince the Peloponnesians that they had simply been unprepared, and would certainly win a second battle:

"There are solid advantages on your side - you have the bigger fleet: you are fighting off your own native shores with hoplites ready to support you. And as a rule the side that wins is the side with the numbers and the equipment. There is not one single reason, therefore, why we should lose." (Thucydides, 2.87)

The Athenians did not want to fight either, seeing that they were outnumbered. Phormio believed that the Athenians were more experienced at sea and could defeat any fleet sent against them, even this larger Peloponnesian fleet:

"Great forces before now have been defeated by small ones because of lack of skill and sometimes because of lack of daring. We are deficient in neither of these qualities." (Thucydides, 2.89)

The Peloponnesians wanted to draw the Athenian ships into the narrowest part of the Gulf, but Phormio intended to fight at Naupactus. However, the Peloponnesians formed four lines, with 20 ships of the right wing pretending to head for Naupactus, which tricked Phormio into moving out in an attempt to stop them. Nine Athenian ships were captured or destroyed in the ensuing skirmish, while the other eleven were able to escape, although the twenty Peloponnesian ships continued to chase them. Ten of the Athenian ships made it to Naupactus, while the eleventh used an offshore merchant ship as a hiding spot. When the lone Peloponnesian ship still in pursuit, under the command of Timocrates, appeared near the merchant ship, the Athenian ship moved out of its hiding spot and sank it. This was an unexpected move and the inexperienced Peloponnesians panicked. The eleven Athenian ships attacked from the safety of the harbour at Naupactus, capturing six Peloponnesian ships and chasing the rest out of the Gulf. Soon after this, the other 20 ships commanded by Nicias arrived at Naupactus, and the Peloponnesians withdrew completely.

A few months later, Cnemus and Brasidas made a surprise attack on Salamis Island and the Athenian port of Piraeus, but they were defeated there as well.

Battle of Naupactus
Conflict	Peloponnesian War
Date	429 BC
Place	Off Naupactus
Result	Athenian victory
Combatants
Athens		Peloponnesians
Commanders
Phormio		Cnemus Brasidas Timocrates Lycophron Machaon Isocrates Agatharchidas
Strength
20 ships		77 ships
Casualties
9 ships		18 ships
Battle before		Battle after
Battle of Chalcis		Battle of Mytilene
Peloponnesian War Sybota - Potidaea - Chalcis - Naupactus - Tanagra - Olpae - Pylos - Sphacteria - Delium - Amphipolis - Mantinea - Sicilian Expedition - Syme - Cynossema - Cyzicus - Notium - Arginusae - Aegospotami - Naxos