The apse has four Ionic pilasters in red jasper, which frame two frescoes by Domenico Canuti, 1684. The frescoes depict the Martyrdom of Nemesius, Exuperia, Sempronius, Olympius, Lucilla and Theodulus. Their relics were brought here in the year 996 by Pope Gregory V and placed under the altar in 1580 by Gregory XIII.