The summer of 429 BC was marked by a
Peloponnesian offensive in the Greek northwest. The
Spartans and their allies hoped to knock several Athenian allies such as
Acarnania,
Zacynthus, and
Cephallenia out of the war, and if possible to capture the Athenian base at
Naupactus. The Spartan
navarch Cnemus was placed in command of the campaign. He set out against Acarnania with 1,000
hoplites from Sparta, crossing over the
Corinthian Gulf unnoticed by the Athenian fleet under
Phormio. Combining his forces with 2,000 troops sent from allied states, Cnemus moved against the Acarnanian city of
Stratus. The Acarnanians appealed to Phormio for help, but he refused to leave Naupactus undefended. The Peloponnesian fleet, meanwhile, was charged with ferrying troops to the southern coast of Acarnania to prevent the residents of that area from supporting their allies inland. As the Peloponnesians moved westward along the south coast of the Gulf of Corinth, the Athenian fleet followed them on the northern shore. The Peloponnesians, with 47 ships, were not particularly concerned about the 20 Athenian ships across the gulf, but they nonetheless left their moorings at night to pass through the strait between
Rhium and Cape
Antirrhium, hoping to give their pursuers the slip. This ruse failed, as the Athenians noticed the move and gave chase, catching the Peloponnesians in the open water of the
Gulf of Patras. ==Battle==