One of the elements I always was fascinated in Dante's Hell was the 6th circle's city of Dis. It is protected, he says, by red hot iron walls, has the shape of a huge fortress, or something such. It's inhabited by dark priests and is filled with flaming tombs of heretics. Going through the city, you reach a stairway, I suppose, a passage that leads you to the entire inner circles of Hell. My hunch is, the artist has read Dante.