The two epics written by Homer the Illiad and the Odyssey are considered to be what's known as Primary epics. The third book written by Virgil, The Aeneid , is considered to be a secondary epic. Why is this?
Basically this is the difference:For Primary EpicNo single author (each is a product of the oral tradition)Written down after centuries of oral transmissionSecondary Epic A single, gifted poet such as Virgil or Milton composes a work that imitates a folk epic. The Æneid and Paradise Lost, for example, involved considerable research and have the style of earlier epics (particularly in setting, dignified speeches, and extended similes.