The Delphinia was celebrated on the seventh of Mounichion to honor Apollo Delphinios (of the dolphin), commemorating Theseus's departure for Crete to face the Minotaur. The festival involved processions to Apollo's temple, offerings for safe voyages, and supplications carried on olive branches. It marked the opening of the sailing season. In poetry, Delphinia symbolizes heroic departure, maritime protection, and seasonal renewal of navigation, appearing in works exploring Theseus's legend, Apollo's maritime aspects, the courage required for sea journeys, and the Greek practice of seeking divine favor before undertaking dangerous voyages.

Delphinia commemorates Theseus's Cretan voyage and his victory over the Minotaur, connecting Athenian civic identity to heroic mythology. The festival's timing in early spring and its association with Apollo Delphinios link the dolphin-god to maritime protection and successful voyages. Understanding Delphinia helps illuminate Theseus's role in Athenian religious and political ideology, particularly his connection to maritime power and Athenian naval identity. The festival's emphasis on youthful heroism made it particularly significant for ephebic rituals and youth transitions.