The battle of Stratus (429 BC) was a Spartan defeat that ended a brief campaign designed to drive the Athenians out of Acarnania, the area to the north-west of the entrance to the Gulf of Corinth (Great Peloponnesian War)
The Spartans were persuaded to launch this expedition by their allies in the north-west of Greece - the Ambraciots and the Chaonians. The plan was for a combined land and naval operation. A Spartan and allied army would invade Acarnania from the Gulf of Ambracia to the north, while their fleet would cruise off the coast in an attempt to prevent the Acarnanians from uniting against the invaders.
The allied army took shape at Leucas, a island just outside the gulf of Ambracia, before moving to the territory of Amphilochian Argos at the eastern end of the gulf. The army consisted of 1,000 Peloponnesians, contingents of Greek troops from Ambracia, Leucas and Anactorium, and local non-Greek troops from the Chaonian, Paravaean and Orestian tribes. The combined army was commanded by the Spartan admiral Cnemus.
Cnemus decided to march south and attack Stratus, the largest town in Acarnania, hoping that a victory there would end resistance across the entire region. His army moved south from Argos, sacked the village of Limnaea, and then moved towards Stratus in three divisions. The Greek troops were on the flanks, with the Ambraciots and Peloponnesians on the left and the Leucadians and Anactorians on the right, while the native troops made up the central division.
Cnemus's plan was for all three divisions to camp close together near to the city, but the Chaonians in the central division decided to try and capture Stratus in a surprise attack. While the two Greek divisions were preparing to camp the Chaonians and the rest of the central division continued on towards the town. The defenders of Stratus realised that they had a chance to defeat part of the invading army, and set a trap. Parties of troops were placed in hiding outside the town. When the Chaonians reached Stratus they were attacked from the town and ambushed from the flanks. The Chaonians broke and fled, taking the rest of the central division with them.
The two Greek divisions were only aware that a battle had been fought and lost when the retreating troops from the central division reached their camps. Cnemus ordered the two Greek divisions to move together to form a single line, while the defeated central division took shelter behind the new line. The more lightly equipped Acarnanias refused to come to close quarters with the hoplites, and instead pelted them with sling stones from a safe distance. On the night after the battle Cnemus was forced to retreat back to the Anapus River, nine miles from Stratus. He was able to arrange an armistice to collect the bodies of the dead, and then retreated back north to safety.
At about the same time as Cnemus's invasion was coming to grief at Stratus part of his fleet was also suffering a defeat, this time at Chalcis, close to the mouth of the Gulf of Corinth.