How did Ovid develop the Heroides into a new literary genre?

Ovid transformed the Heroides into a new literary genre by adapting existing concepts into a series of dramatic monologues written in elegiac couplets.1

While the idea of letters from legendary figures had been used previously by poets such as Sextus Propertius, Ovid elevated the form by applying his rhetorical training—specifically the exercises known as ethopoiea, or "character drawing"—to give voice to mythological women like Penelope, Dido, and Ariadne.1

He further refined this genre in the later epistles of the collection by introducing a paired structure, where a lover and his correspondent exchange letters, allowing for an ingenious and interactive treatment of their literary sources. Through this approach, Ovid moved beyond simple imitation, utilizing his rhetorical brilliance to create a distinct and influential format.1