Epic is a type of poem, usually describing the heroic exploits of a character, and the narrative story is important to the culture and history of a nation or people. The poem is usually written in a rule-bound metric structure such as dactylic hexameter and touches on themes of central importance to a people. Epic poems were usually lengthy, often accompanied by music, and when recited were a lesson in shared history. Poems which were described as epics include the Epic of Gilgamesh of unknown origin (there are many versions circulating), Iliad and Odyssey by the Greek poet Homer, Theogony by Hesiod, Ramayana ascribed to Valmiki, the Aeneid by Virgil, the story of Beowolf, and numerous other works.