Descent into Hell!!! Rarrr!...Well, sort of...

[Eruanna]

Lalwendë said:

I often wonder if the symbolism of Moria is intended to be similar to the idea of Dante's levels of Hell. Moria has halls and levels, it has it's own 'satan' in the figure of the Balrog, and demons in the form of the Orcs, and it is clearly a place where untold suffering has happened.

I have always thought that this held true.
As well as the symbols mentioned by Lalwendë there are other pointers.
The mere mention of Moria fills all of the fellowship with an unnamed dread. With the exeption of Gimli, of course, and yet even he is described as "...a smouldering fire was in his eyes". What could be more 'hellish' for an Elf, than to spend days and nights in a place where the sun or the stars never shine.
In the myths and legends of many cultures, Hell or the Underworld is reached by crossing water. At the entrance to Moria we have Sirannan, the Gate-stream.
There is also the Watcher in the Water. A twisted, snake-like, many limbed guardian of the entrance to the Underworld, like the many headed Cerberus perhaps?
Another symbol that struck me recently, is the mention of the holly that marks the entrance to the Gate. Holly was the symbol of the people of Hollin, who used the gate, to be sure. However, holly is an important plant in both Pagan and later Christian beliefs. In medieval times holly leaves would be placed around tombs, as a talisman against witchcraft and as a warning that evil spirits lurked.
On the other hand, Frodo and Sam's journey in Mordor always makes me think of a sort of purgatory, an ante-room if you will, to be endured before the actual fiery hell of Mount Doom, and Frodo, Sam and Gollum's eventual release or death.