This circle houses the violent.
Its entry is guarded by the Minotaur, and it is divided into three rings:

Outer ring,
housing the violent against people and property, who are immersed in Phlegethon, a river of boiling blood, to a level commensurate with their sins. The Centaurs, commanded by Chiron, patrol the ring. The centaur Nessus guides the poets along Phlegethon and across a ford in the river. (Canto XII)

Middle ring:
In this ring are the suicides, who are transformed into gnarled thorny bushes and trees. They are torn at by the Harpies. Unique among the dead, the suicides will not be bodily resurrected after the final judgment, having given their bodies away through suicide. Instead they will maintain their bushy form, with their own corpses hanging from the limbs. Dante breaks a twig off of one of the bushes and hears the tale of Pier delle Vigne, who committed suicide after falling out of favor with Emperor Frederick II.

The other residents of this ring are the profligates, who destroyed their lives by destroying the means by which life is sustained (i.e. money and property). They are perpetually chased by ferocious dogs through the thorny undergrowth. (Canto XIII) The trees are a metaphor; in life the only way of the relief of suffering was through pain (i.e. suicide) and in Hell, the only form of relief of the suffering is through pain (breaking of the limbs to bleed).

Inner ring:
The violent against God (blasphemers), the violent against nature (sodomites), and the violent against art (usurers), all reside in a desert of flaming sand with fiery flakes raining from the sky. The blasphemers lie on the sand, the usurers sit, and the sodomites wander about in groups. Dante converses with two Florentine sodomites from different groups: Brunetto Latini, a poet; and Iacopo Rusticucci, a politician. (Cantos XIV through XVI) Those punished here for usury include Florentines Catello di Rosso Gianfigliazzi, Ciappo Ubriachi, and Giovanni di Buiamonte, and Paduans Reginaldo degli Scrovegni and Vitaliano di Iacopo Vitaliani.

The Divine Comedy - Inferno
Dante Aligheri