Battle of Rhium The Battle of Rhium ( 429 BC ) or the battle of Chalcis was a naval battle in the Peloponnesian War between an Athenian fleet commanded by Phormio and a Peloponnesian fleet composed of contingents from various states , each with its own commander . The battle came about when the Peloponnesian fleet , numbering 47 trireme s , attempted to cross over to the northern shore of the Gulf of Patras to attack Acarnania in support of an offensive in northwestern Greece ; Phormio ' s fleet attacked the Peloponnesians while they were making the crossing . In the battle , the Peloponnesian ships , hampered by the fact that many of them were equipped not as fighting vessels but as transports , circled together in a defensive posture . Phormio , taking advantage of his crews ' superior seamanship , sailed around the clustered Peloponnesians with his ships , driving the Peloponnesians closer and closer together until they began to foul oars and collide with each other . The Athenians then suddenly attacked , routing the Peloponnesians and capturing 12 ships . Prelude . 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 Phormio . Combining his forces with 2 , 000 troops sent from allied states , Cnemus moved against the city of Stratus , an Acarnanian ally . 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 Athenians 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 . Although the Peloponnesian fleet was numerically superior to the Athenian , many of its ships were rigged out as transports instead of fighting vessels . Thus , as the Athenian fleet approached them , the Peloponnesian commanders ( the names of all of these are not known , but the Corinthian commanders were Machaon , Isocrates , and Agatharchidas ) ordered their 47 trireme s to draw into a circle , prows outward , for defense . In the center of the circle were gathered the smaller ships and the five fastest triremes , which were to plug any gap that opened in the circle . Phormio chose to attack this formation by using a risky and unorthodox tactic . He led his ships , in line , in a tightening circle around the Peloponnesians , darting inwards at times to drive the defending ships closer to each other . This tactic left the Athenians highly vulnerable to a swift attack , as any of the defending ships would only have to move a short distance straight ahead to ram a circling Athenian ship in the side . No such attack materialized , however , and the Peloponnesians were driven closer and closer together . At this point , Phormio was aided by his experience with the local weather patterns , which had taught him that a wind usually blew out of the gulf at dawn . Expecting that this wind would severely discomfort the inexperienced Peloponnesians but not interfere at all with the work of his own more experienced crews , he waited for the moment it arose to attack . As expected , when the wind blew up the Peloponnesian ships were driven together ; confusion reigned in the circle , with steersmen shouting and cursing , oars fouling between ships , and crews attempting to shove off from each other ' s ships with poles . At this moment the Athenians rushed in to attack . The rout was instant and total ; the Peloponnesians , in their short flight to the southern shore , saw 12 of their ships , with crews , captured by the pursuing Athenians . Aftermath . On the way back to their base at Corinth , the Peloponnesian fleet met up with Cnemus , who was retreating from a defeat by the Stratians . This double defeat seriously embarrassed Cnemus , and was in general an embarrassing failure for the Spartans ; their first attempt at an amphibious offensive had ended in ignominy . The victory did not , however , put an end to the Peloponnesian offensive in the Gulf . Within a short period of time the Spartans were able to assemble a substantially larger fleet , this time of 77 triremes ; Athens , meanwhile , though it dispatched 20 ships to reinforce Phormio , sent them by way of Crete . Thus , Phormio ' s 20 ships were forced to fight on their own , and only narrowly preserved Athenian dominance in the gulf at the Battle of Naupactus .