The altar is monochrome, in white marble. A pair of Ionic columns with swagged capitals support a little triangular pediment. Below the altar is a 4th century alabaster basin behind a grille in the same style as that protecting the miraculous column. It was found in the Bernini restoration in 1624 buried beneath the sanctuary floor, and was then used to enshrine the relics of SS Bibiana, Dafrosa and Demetria.