Writers have been using allegory as a literary device for centuries. Artists, as well, use this device within abstract portraits to express complex concepts from the real world. Defined as an extended metaphor that's carried out through the length of a story, allegory uses characters, themes, locations or any number of story components to represent an underlying meaning.
What distinguishes this literary device from other forms is the detail in which the underlying concept is portrayed through prose. And while other devices are more logic-driven, allegory is meant to appeal to the reader's imagination. Concepts like religion, politics, morals and values often make up the underlying meanings found in the more well-known writings.
The Bible is filled with allegorical accounts, both in the old and new testaments. This method of conveying complex ideas and concepts was a standard teaching model throughout biblical times as well as the Middle Ages.
In ancient Greece, allegory was expressed in three forms: fables, parables and apologues. Apologues are short stories that use narrative details to convey a point of view. The stories are constructed for the sake of rhetorical argument, with emphasis placed on the moral of the story rather than narrative details.
Fables are also short stories, but the characters appear as animals, things, plants or forces of nature. The characters are also given human abilities like speech and thought. A popular example of this type is "Aesop's Fables," where the story typically ends with a moral statement of purpose.
Parables are much like fables in that a moral or religious lesson is portrayed, but the characters in parables are human. The New Testament contains many parables as spoken by Jesus Christ, two of which are "The Good Samaritan" and "The Prodigal Son."
The word "allegory" comes from the Greek and literally means "speaking otherwise." The more general definition is "to speak figuratively." Greek plays made exclusive use of the devise to teach lessons on religious values, and the plays themselves were actually called allegories. Early Christianity also made use of allegorical references to present a new religious system of morals and values.
Allegory appears throughout the Middle Ages in the forms of prose, narrative, theatrical works and art. Its use served as a tool to integrate the history of the ancient world with the world of the Middle Ages. It wasn't until 400 CE when Prudentius, a philosopher, wrote "Psychomachia," the first literary work defined as purely allegorical in origin.
Modern day use of allegory is not only reflected in writings and artwork, but also in film. Examples of modern allegorical works include books such as "Animal Farm," "The Last Unicorn" and "A Prayer for Owen Meany," and films such as "The Matrix," "El Topo" and "The Seventh Seal."