The columns support horizontal entablatures rather than arches, which makes the church look much older than it is, the arrangement is called a trabeation. The columns seem to come from a variety of sources. Eight 3rd-century Ionic capitals with images of Isis, Serapis, and Harpocrates, now in the nave colonnades, were taken from one or both of the rooms currently identified as libraries in the Baths of Caracalla. The capitals were transferred around 1140, when the church was rebuilt by Pope Innocent II.