How does the Inferno reflect both the Christian and Greco-Roman traditions?

The existence of an Inferno (Hell) is an element of the
Christian tradition as is the belief in the Holy Trinity. This belief informs the very
structure of the Inferno (there are nine circles and the narrative is divided in 33
cantos, plus an introductory canto to the entire Comedy). There are
also important references to the Bible and Christian theology. Dante's interpretation of
human history is always Christian in nature. This is what Auerbach calls "figural" or
"typological" procedure. In this conception, historical events and characters dating
back to before the advent of Christianity ultimately represent and pre-figure events and
characters belonging to Christianity. For example, the Roman Empire of Augustus which
had its official poet in Virgil is read by Dante as an image of God's Kingdom. This
procedure was not invented by Dante, but is at the heart of Christianity itself and
theologians have explained the relationship of the Old and New Testaments through this
concept.

Yet, in Dante's Inferno, Greco-Roman traditions
and beliefs are important too. The order of the sinners and the idea of evil are
borrowed from Greek and Roman culture and are particularly indebted to Aristotle. In
addition, Dante's conception of the universe is clearly derived from the Ptolemaic
tradition with the Earth at the center. In this case, however, there is no contrast
between the Greco-Roman and Christian traditions as the Church adopted the Ptolemaic
model of the universe.

Finally, it shouldn't be surprising
that the Inferno and the entire Commedia have
both Greco-Roman and Christian elements. Dante's oeuvre was thought as a summa
of all cultural traditions and philososphical beliefs that constituted
Middle-Ages knowledge.