The Circles of Hell are the realms which Dante must travel through on his quest to save Beatrice.
There are 9 Circles of Hell (10 including the Shores of Acheron) and are crossed through in the following order:
Circle[]
The 9 Circles of Hell
Limbo[]
Lust[]
Gluttony[]
Greed[]
Anger[]
Heresy[]
Violence[]
Fraud[]
Treachery[]
Each Circle has its own special setting and Creatures which Dante has to defeat in order to reach Lucifer in the Circle of Treachery