Spanning much of the third quarter of the century, the pontificates of Benedict III (855–858), Nicholas I (858–867) and Hadrian II (867–872) reveal a declining papal involvement in the patronage of architecture, though also considerable engagement with ecclesiastical issues of the day, including dramatically renewed contacts with Constantinople and the eastern Mediterranean in the aftermath of the definitive end of Byzantine Iconoclasm and the ‘Triumph of Orthodoxy’. In addition to the growing importance of the Roman secular aristocracy, whose domestic housing has been rediscovered in recent archaeology, evidence is surveyed for the continuing presence of a substantial Greek community in Rome, and for interest in the translation of Greek texts in the circle of the papal librarian, Anastasius. Among the most prominent survivals from these years is the tomb of St Cyril, the Byzantine missionary to the Slavs, in the lower church of San Clemente.

The shock occasioned by the Arab sack of Saint Peter’s and San Paolo fuori le mura in August 846 serves as the backdrop for the unprecedented building activities of Pope Leo IV (847–855), best known for his construction of fortifications to enclose the entire area around Saint Peter’s in what subsequently came to be known as the ‘Leonine city’. This was the only extension ever made to Rome’s Aurelian walls of the late third century. Considerable resources were also expended on making good the losses of gold and silver liturgical vessels, silk textiles and other furnishings. New church projects included Santi Quattro Coronati and Santa Maria Nova. Also dating from his reign, and signalling a shift in patronage to become more evident in the years to follow, is a subsidiary chapel in the excavated lower church of San Clemente, which includes the pope’s portrait. Consideration is given to the rationale for the installation of this chapel, possibly with a relic from the site of Christ’s Ascension prominently displayed above its altar.