There is a very interesting article on the New Liturgical Movement about the church of San Clemente in Rome by Dino Marcantonio which explains the iconography and symbolism of the building and its decoration.
The interior of San Clemente
A view of the nave, the schola cantorum with the ambos to either side,
the altar and confessio under the ciborium,
and the bema at the back of the apse.
It is well worth looking at and, if you have not already seen it, can be read here.