The Theseia was an Athenian festival commemorating Theseus, the city's legendary king and civilizing hero who defeated the Minotaur and unified Attica. Celebrated on the eighth day of Pyanepsion, it featured athletic competitions, sacrifices, and processions to his shrine. The festival reinforced Athenian identity through heroic mythology. In poetry, Theseia represents heroic ideals, civic foundation myths, and the transformation of legendary figures into civic patrons, appearing in works exploring Athenian identity, heroic virtue, the relationship between myth and political legitimacy, and the role of ancestral heroes in communal self-definition.

Theseia honored Athens's hero Theseus, celebrating his legendary deeds and his role as Athens's founding king. The festival emphasized Theseus's civilizing achievements, military victories, and political unification of Attica. Understanding Theseia helps contextualize hero worship's importance in Athenian civic ideology and how legendary figures sanctified political institutions. The festival demonstrates how Athens used religious commemoration to reinforce civic identity and legitimate contemporary political arrangements through connection to heroic foundations.