Notes from Antiquity explains that Greek poems and plays were actually musicals:
Greek poets and dramatists regularly set their work to music themselves, and from at least the fifth century B.C. on they used a highly sophisticated system of musical notation. The very idea of poetry, in fact, originally tended to imply music, and Athenian tragedy at its artistic peak, in the fifth century B.C., was a complex combination of poetic text, solo and choral song, recitation with instrumental accompaniment, and dance. This has an unsettling if little-recognized implication: watching a play by Euripides or reading poetry by Sappho is perhaps as incomplete an experience today as watching a ‘play’ by Wagner or reading ‘poetry’ by Stephen Sondheim would be.
(Hat tip to 2blowhards.)