An epic is a genre of narrative poetry that tells the story of a heroic figure of national importance. Epics are characterized by their great length, multiple settings, large casts of characters, and spans of time. They often involve characters from history or legend undertaking heroic deeds, and include involvement of gods or spirits. Epics are public poetry that express the thoughts and feelings of a large group, and celebrate deeds of valor by giants among men with superhuman power who act as heroes. Epics follow certain conventions including invocations, Homeric similes, athletic contests, dangerous journeys by heroes, and stories within the main action.