In Limbo reside the unbaptized and the virtuous pagans, who, though not sinful, did not accept Christ. Limbo shares many characteristics with the Asphodel Meadows; thus the guiltless damned are punished by living in a deficient form of Heaven. Without baptism ("the portal of the faith that you embrace") they lacked the hope for something greater than rational minds can conceive. Limbo includes green fields and a castle with seven gates to represent the seven virtues. The castle is the dwelling place of the wisest men of antiquity, including Virgil himself, as well as the Persian polymath Avicenna. In the castle Dante meets the poets Homer, Horace, Ovid, and Lucan; the Amazon queen Penthesilea; the mathematician Euclid; the scientist Pedanius Dioscorides; the statesman Cicero; the first doctor Hippocrates; the philosophers Socrates, Plato, Aristotle, and Averroes; the historical figures Lucretia, Lucius Junius Brutus, and Julius Caesar in his role as Roman general ("in his armor, falcon-eyed"); mythological characters Hector, Electra, Camilla, Latinus, and Orpheus; and many others. Interestingly, he also sees Saladin in Limbo (Canto IV). Dante implies that all virtuous non-Christians find themselves here, although he later encounters two (Cato of Utica and Statius) in Purgatory and two (Trajan and Ripheus) in Heaven.
      Beyond the first circle, all of those condemned for active, deliberately willed sin are judged to one of the lower eight circles by the serpentine Minos. Minos initially hinders the poets' passage, until rebuked by Virgil. Minos sentences each soul by wrapping his tail around himself a corresponding number of times. The lower circles are structured according to the classical (Aristotelian) conception of virtue and vice, so that they are grouped into the sins of wantonness, violence, and fraud (which for many commentators are represented by the leopard, lion, and she-wolf). The sins of wantonness – weakness in controlling one's desires and natural urges – are the mildest among them, and, correspondingly, appear first, while the sins of violence and fraud appear lower down.

Taken from Dante's Inferno on Wikipedia