IN 609, THE BYZANTINE EMPEROR PHOCAS, WHO CONTROLLED ROME through the Exarchate, gave the Pantheon to Pope Boniface IV (608–615) at his request. The pagan temple dedicated to all the gods was immediately rededicated to St. Mary and to all the martyred saints. S. Maria ad martyres, which we now call S. Maria della Rotonda, was named a stational church, meaning that the faithful joined to celebrate a particular day in the saints’ calendar – in this case, 1 November, All Saints Day, followed by All Souls Day. Thus the church became an important destination; indeed it is listed 5th of 26 churches in a seventh-century itinerary, De locis sanctis martyrum (Fig. 121).

The Pantheon, as S. Maria, was now under the protection of the Church, which took responsibility for its maintenance. Thus when the Byzantine emperor Constans II stripped off its bronze roof tiles in 663 to take back to Constantinople, Pope Gregory III (731–741) had them replaced with sheets of lead for protection. His restoration set a precedent of pastoral care that lasts to this day. S. Maria continued to use the colonnaded forecourt adjoining it to the north as a place to assemble before entering the sanctuary. Even through centuries of flooding and silting, it was cleaned and maintained until the tenth century.

The Pantheon was not the only ancient monument to gain new purpose during the medieval period. A charitable institution providing food, shelter, and bathing facilities for the poor, the diaconia, probably arrived with the Greek colony. It and related urban services including xenodochia (charitable institutions providing food and shelter), gerocomia (old-age homes), and ptochia (poorhouses) often took advantage at one time or another of modest ancient structures that had few ambitious formal functions of their own. As monasteries and churches did, the diaconia played a vital role providing social services to the poor and to pilgrims.

Diaconiae often served more than one purpose, and their programs changed over time. For example, some of them administered hospitals, so at some point in its history an individual diaconia might assume the care of the sick within its own walls rather than run a separate organization under its supervision.