This unusual centrally planned church, known in the Middle Ages as S Stefano in Celio, was consecrated by Pope Simplicius (reigned 468-483). The original design took the form of a circle (diam. 65 m), around which ran two concentric ambulatories. The outer circle contained four radiating arms and four bipartite atria, each of which had two points of access, resulting in a cruciform structure set within a perfectly circular perimeter that has sometimes been compared to that of the Holy Sepulchre in Jerusalem. Major restoration works were begun by Innocent II (reigned 1130-1143). Even more radical restorations were begun under Nicholas V, who engaged Bernardo Rossellino to eliminate the outer ring, reduce the diameter to 40 m and remove two of the four arms of the Greek cross. The interior still has 7th century mosaics.