It has two pairs of gigantic ribbed Composite columns in red marble with gilded ribs, supporting the halves of a split segmental pediment, on which sit two angels executed by Guillaume Berthelot from a design by Camillo Mariani. Into the gap between the halves is inserted a gilded relief panel with its own little segmental pediment, which depicts Pope Liberius and the Miracle of the Snow, by Stefano Maderno. The altar itself, in the form of an ancient sarcophagus in lapis lazuli with bronze fittings, is 18th century. The side walls flanking the altar have statues below the cantorie.