The traditional or folk epics are based upon legend and history preserved through oral traditions. Such epics include Homer's Iliad and Odyssey and the medieval epic Beowulf. Literary epics are learned imitations of the traditional form, such as Virgil's Aeneid and Milton's Paradise Lost (1667).
Some recurring features of the structure and action of classical epics have come to be viewed as epic conventions. Structurally, the epic begins with a statement of the poem's "argument" (subject matter), proceeds to an invocation to a muse or divine source of inspiration, and then jumps into the action in medias res ("in the middle of things"). Earlier events are later recounted in narrative flashbacks.
Other epic conventions include the arming of the hero, extraordinary deeds of battle, a great journey (including a descent to the underworld), and the active intervention of gods or supernatural beings.
By extension, the term "epic" is also applied to novels, dramas, and films which have epic grandeur in the scale of their action or the importance of their subject to human society at large. (See also mock epic. )