Phaedra is an adaptation of an old Greek myth from the collection of traditions involving Theseus, arguably the principal hero of Athens. The myth tells of Phaedra’s doomed love of her stepson Hippolytus, which leads to the unhappy deaths of both Hippolytus and Phaedra. Seneca’s main source was most likely Euripides’s Hippolytus, a Greek tragedy produced in 428 BCE.

Euripides composed two Hippolytus tragedies. To distinguish between them, the earlier of the two is often known as Hippolytus Veiled (Hippolytos Kalyptomenos in Greek) while the second is known as Hippolytus Crowned (Hippolytos Stephanephoros in Greek), or simply Hippolytus. Of these two plays, only the latter survives. The original play, Hippolytus Veiled, was probably produced in the mid-430s BCE. For reasons that are unclear (only fragments of the play survive), the first Hippolytus was condemned as immoral when it was first staged. This prompted Euripides to produce a second Hippolytus in 428 BCE. This play, which has survived intact, was much praised in antiquity and awarded the first prize. It is still widely read and admired today.

Euripides’s second surviving Hippolytus told a slightly different version of the myth from that told by Seneca in Phaedra.