Poetic narratives are poems that have a plot, such as Edmund Spencer’s The Faerie Queen, John Milton’s Paradise Lost, The Romance of the Rose, Tennyson’s Idylls of the King, Robert Browning’s The Ring and the Book, Chaucer’s Canterbury Tales, etc. Some scholars believe that Homer compiled the Iliad and the Odyssey from a collection of shorter narrative poems that took the form of the various episodes or adventures that appear in these longer works. Ballads are a type of narrative poetry. Some of Edgar Allen Poe’s works are narrative poetry (The Raven, Annabel Lee, etc.) Other famous narrative poets are Ovid, Dante, Chaucer.
Narrative poetry is probably one of the oldest forms of poetry (i.e. the heroic epic poetry represented by works such as Beowulf). Before writing, the only way to transmit stories was through oral tradition. Hero tales were passed from one generation to the next. In order to more readily remember the tales, storytellers used poetic forms because rhyme and rhythm makes things easier for the human brain to memorize. That is why it is easier for us to remember the words to songs than to remember all presidents of the United States. In fact, many mnemonic devices are employed when trying to memorize things. These include rhymes, poetry and songs.
Although many of the works mentioned above are lengthy, narrative poems are not necessarily so. Allegory is a way of conveying a meaning in ways that are not literal. Allegory conveys its meaning through use of symbolism which can take the form of symbolic figures, actions or representations. An allegory is an extended metaphor and therefore uses other poetic devices to convey the meaning – onomatopoeia, simile, imagery, irony, ambiguity, and elements of style such as assonance, alliteration, rhythm, diction, etc.
In light of the above, I believe it is a true statement to say that allegory is a universal element of poetic narrative. Not all poetic narratives are allegories, but many of them are or at least contain elements of allegory.
You originally had your question posted in the ARTS group. Allegory does exist in art, but that would be a different answer.