Battle of Cynossema The naval Battle of Cynossema ( Ancient Greek : ) took place in 411 BC during the Peloponnesian War . In the battle , an Athenian fleet commanded by Thrasybulus and Thrasyllus , although initially thrown on the defensive by a numerically superior Spartan fleet , won a narrow victory . This victory , coming as it did at a time when Athens ' traditional democratic government had been replaced by an oligarchy , and when an Athenian defeat could have ended the war , had an impact out of proportion to its tactical significance . The newly confident Athenian fleet proceeded to win two more victories in the Hellespont in quick succession , the second being the dramatic rout at Cyzicus , which ended the immediate Spartan threat to Athens ' Black Sea lifeline . Prelude . In the wake of Athens ' defeat in the Sicilian Expedition in 413 , a small Spartan fleet commanded by Chalcideus , who was advised and assisted by Alcibiades , succeeded in bringing a number of critical Ionian cities into revolt from the Athenian Empire . After the revolt of the critical city of Miletus , the Persian satrap Tissaphernes concluded an alliance against Athens with Sparta . The Spartans remained unwilling to challenge the Athenians at sea , and an Athenian fleet succeeded in recapturing several cities and besieging Chios during the later months of 412 BC . In 411 BC , however , further rebellions at Rhodes and Euboea , and the capture of Abydos and Lampsacus on the Hellespont by a Peloponnesian army that had marched there overland , forced the Athenians to disperse their forces to meet these various threats . The Spartan fleet could now move freely in the Aegean , and took advantage of its newfound superiority by lifting the blockade of Chios and bottling up the Athenians ' Aegean fleet at Samos . By withdrawing their ships from the Hellespont to Samos , the Athenians were able to reestablish their naval superiority in the Aegean , but in doing so they opened the door for Sparta to shift the theater of war . Accordingly , in late July , the Spartan commander Clearchus made an attempt to slip 40 ships past the Athenian fleet to the Hellespont . These were turned back by a storm , but shortly afterwards 10 ships under the Megarian general Helixus reached the Hellespont , where they triggered revolts in Byzantium , Chalcedon and other important cities . Several months later , the new Spartan navarch Mindarus , deciding that the promises of support made by Pharnabazus , the Persian satrap of Anatolia , were more promising than those of Tissaphernes in Ionia , slipped his entire fleet past the Athenians . He joined up with the Peloponnesian ships already operating in the Hellespont and established his base at Abydos , forcing the small Athenian fleet at Sestos to flee , with losses , to Imbros and Lemnos . Battle . With a substantial Peloponnesian fleet operating in the Hellespont , the crucial trade route through which Athens ' grain supply passed , the Athenian fleet had little choice but to pursue Mindarus . Accordingly , Thrasybulus , assuming overall command , led the fleet to Elaeus on the tip of the Gallipoli peninsula , where the Athenians spent five days preparing to challenge the 86 Spartan ships at Abydos with their 76 ships . The Athenian fleet sailed in column into the Hellespont , following the northern shore , while the Spartans put out from Abydos on the southern shore . When the Athenian left had rounded the point of Cynossema , the Spartans attacked , planning to outflank the Athenian right and trap the fleet in the Hellespont while driving the center aground on Cynossema . The Athenian center was quickly driven aground , and the left under Thrasyllus , beset by Syracusan ships and unable to see the rest of the fleet around the sharp point , was unable to come to its aid . Thrasybulus on the right , meanwhile , was able to avoid encirclement by extending his line westward , but in doing so lost touch with the center . With the Athenians divided and a substantial portion of their fleet incapacitated , a Spartan victory seemed assured . At this critical juncture , however , the Peloponnesian line began to fall into disorder as ships broke line to pursue individual Athenian vessels . Seeing this , Thrasybulus turned his ships abruptly and attacked the Spartan left . After routing these ships , the Athenian right bore down on the Peloponnesian center , and , catching them in a state of disorganization , quickly routed them as well . The Syracusans on the right , seeing the rest of their fleet in flight , abandoned their attack on the Athenian left and fled as well . The narrowness of the straits , which ensured that the Peloponnesians had only a short way to go to safety , limited the damage the Athenians could inflict , but by day ' s end they had captured 21 Spartan ships to the 15 of theirs that the Spartans had taken in the early fighting . The Athenians set up a trophy on Cynossema and put in at Sestos , while the Peloponnesians made their way back to Abydos . Aftermath . In the days after the battle , the Athenians refitted their ships at Sestos and dispatched a small detachment to Cyzicus , recapturing that town and seizing 8 triremes encountered along the way . A trireme was dispatched to Athens , where the unexpected good news restored the people ' s confidence in the war effort . Historian Donald Kagan has emphasized the effect this victory had on the Athenians . Forced to fight on terms chosen by their enemies , at a time when the city lacked the resources to build another fleet , the Athenians could have lost the war on that day at Cynossema . Instead , they won a victory that allowed them to continue fighting , with victory still seeming possible .