The original main altar is true white marble. It has columns consisting of a base of golden Siena marble and inset panels of white and light purple breccia. The altar platform is a slightly different white marble. The colonnade behind the original main altar is composed of several types of marble. The base is Verde Antique.
Large pillars are a yellowish breccia, smaller pillars are a white breccia with gray veining.
The wall beneath the pillars and railing is golden Siena marble with insets of a white breccia with purplish veining. Some parts of the balustrade are plaster.