The battle of Cynossema, in 411 BCE, was an Athenian victory during the final years of the Peloponnesian War. It marked the resilience of the renowned Athenian democratic system after their major defeats in Sicily and also after a small civil war within Athens. This victory, narrated by the famous Ancient Greek historian Thucydides, was crucial for the maintenance and balance of power in the Aegean Sea which was the main theatre of combat in the concluding years of the conflict. This defeat over the Spartan fleet demonstrated the utmost strategic importance the Athenians gave to the Hellespont straight which functioned as one of the major arteries for their empire and the Delian League.
This is a companion discussion topic for the original content at https://www.worldhistory.org/article/1400/the-battle-of-cynossema/.