An epic poem, epic, epos, or epopee is a lengthy narrative poem, ordinarily involving a time beyond living memory in which occurred the extraordinary doings of the extraordinary men and women who, in dealings with the gods or other superhuman forces, gave shape to the moral universe that their descendants, the poet and his audience, must understand to understand themselves as a people or nation.
Another type of epic poetry is epyllion (plural: epyllia), which is a brief narrative poem with a romantic or mythological theme. The term, which means "little epic", came into use in the nineteenth century. It refers primarily to the erudite, shorter hexameter poems of the Hellenistic period and the similar works composed at Rome from the age of the neoterics; to a lesser degree, the term includes some poems of the English Renaissance, particularly those influenced by Ovid. The most famous example of classical epyllion is perhaps Catullus 64.
The oldest epic recognized is the Epic of Gilgamesh (c. 2100 BC), which was recorded In ancient Sumer during the Neo-Sumerian Empire. The poem details the exploits of Gilgamesh, the king of Uruk. Although recognized as a historic figure by historians, Gilgamesh, as represented in the epic, is a largely legendary or mythical figure.
The longest epic written is the ancient Indian Mahabharata, which consists of 100,000 ślokas or over 200,000 verse lines (each shloka is a couplet), as well as long prose passages, so that at about 1.8 million words it is about four times the length of the Rāmāyaṇa, and roughly roughly ten times the length of the Iliad and the Odyssey combined.
Famous examples of epic poetry include the Sumerian Epic of Gilgamesh, the ancient Indian Mahabharata and Ramayana, the Tamil Silappatikaram, the Persian Shahnameh, the Ancient Greek Odyssey, Virgil's Aeneid, the Old English Beowulf, Dante's Divine Comedy, the Finnish Kalevala, the German Nibelungenlied, the French Song of Roland, the Spanish Cantar de mio Cid, Camões' Os Lusíadas, and John Milton's Paradise Lost.
Originating before the invention of writing, epics were elaborated by bards who used complex rhetorical and metrical schemes by which they could memorize the epic as received in tradition and add to the epic in their performances. Hence aside from writers like Dante, Camões, and Milton, Apollonius of Rhodes in his Argonautica and Virgil in Aeneid adopted and adapted Homer's style and subject matter, but used devices available only to those who write, and in their works Nonnus' Dionysiaca and Tulsidas' Sri Ramacharit Manas also used stylistic elements typical of epics.
The English "epos" is likewise from the Latin epos, from Greek ἔπος, epos
The first epics were products of preliterate societies and oral history poetic traditions. Oral tradition was used alongside written scriptures to communicate and facilitate the spread culture. In these traditions, poetry is transmitted to the audience and from performer to performer by purely oral means. Early twentieth-century study of living oral epic traditions in the Balkans by Milman Parry and Albert Lord demonstrated the paratactic model used for composing these poems. What they demonstrated was that oral epics tend to be constructed in short episodes, each of equal status, interest and importance. This facilitates memorization, as the poet is recalling each episode in turn and using the completed episodes to recreate the entire epic as he performs it. Parry and Lord also contend that the most likely source for written texts of the epics of Homer was dictation from an oral performance.
Milman Parry and Albert Lord have argued that the Homeric epics, the earliest works of Western literature, were fundamentally an oral poetic form. These works form the basis of the epic genre in Western literature. Nearly all of Western epic (including Virgil's Aeneid and Dante's Divine Comedy) self-consciously presents itself as a continuation of the tradition begun by these poems. Classical epic poetry employs a meter called dactylic hexameter and recounts a journey, either physical (as typified by Odysseus in the Odyssey) or mental (as typified by Achilles in the Iliad) or both. Epics also tend to highlight cultural norms and to define or call into question cultural values, particularly as they pertain to heroism.
In A Handbook to Literature (1999), Harmon and Holman define an epic:
Epic: a long narrative poem in elevated style presenting characters of high position in adventures forming an organic whole through their relation to a central heroic figure and through their development of episodes important to the history of a nation or race. (Harmon and Holman)
An attempt to delineate ten main characteristics of an epic:
The hero generally participates in a cyclical journey or quest, faces adversaries that try to defeat him in his journey and returns home significantly transformed by his journey. The epic hero illustrates traits, performs deeds, and exemplifies certain morals that are valued by the society the epic originates from. Many epic heroes are recurring characters in the legends of their native culture.
Conventions of epics:
Many verse forms have been used in epic poems through the ages, but each language's literature typically gravitates to one form, or at least to a very limited set. Ancient Sumerian epic poems did not use any kind of poetic meter and lines did not have consistent lengths; instead, Sumerian poems derived their rhythm solely through constant repetition, with subtle variations between lines. Indo-European epic poetry, by contrast, usually places strong emphasis on the importance of line consistency and poetic meter. Ancient Greek and Latin poems were written in dactylic hexameter. Old English, German and Norse poems were written in alliterative verse, usually without rhyme. Italian, Spanish and Portuguese long poems were usually written in terza rima  or especially ottava rima. From the 14th century English epic poems were written in heroic couplets, and rhyme royal, though in the 16th century the Spenserian stanza and blank verse were also introduced. The French alexandrine is currently the heroic line in French literature, though in earlier periods the decasyllable took precedence. In Polish literature, couplets of Polish alexandrines (syllabic lines of 7+6 syllables) prevail. In Russian, iambic tetrameter verse is the most popular. In Serbian poetry, the decasyllable is the only form employed.