Ovid works his way through his subject matter, often in an apparently arbitrary fashion, by jumping from one transformation tale to another, sometimes retelling what had come to be seen as central events in the world of Greek mythology and sometimes straying in odd directions. The poem is often called a mock-epic. It is written in dactylic hexameter, the form of the great heroic and nationalistic epic poems, both those of the ancient tradition (the Iliad and the Odyssey) and of Ovid's own day (the Aeneid of Virgil). It begins with the ritual "invocation of the muse", and makes use of traditional epithets and circumlocutions. But instead of following and extolling the deeds of a human hero, it leaps from story to story with little connection.