The Aeneid is widely considered Virgil's finest work and one of the most important poems in the history of western literature. Virgil worked on the Aeneid during the last eleven years of his life (29–19 BC), commissioned, according to Propertius, by Augustus. The epic poem consists of 12 books in dactylic hexameter verse which describe the journey of Aeneas, a warrior fleeing the sack of Troy, to Italy, his battle with the Italian prince Turnus, and the foundation of a city from which Rome would emerge. The Aeneid's first six books describe the journey of Aeneas from Troy to Rome. Virgil made use of several models in the composition of his epic; Homer, the preeminent author of classical epic, is everywhere present, but Virgil also makes special use of the Latin poet Ennius and the Hellenistic poet Apollonius of Rhodes among the various other writers to which he alludes. Although the Aeneid casts itself firmly into the epic mode, it often seeks to expand the genre by including elements of other genres such as tragedy and aetiological poetry. Ancient commentators noted that Virgil seems to divide the Aeneid into two sections based on the poetry of Homer; the first six books were viewed as employing the Odyssey as a model while the last six were connected to the Iliad.