Roman monasticism in the early middle ages presents a paradox. ‘No other city in Christendom, save perhaps Constantinople, witnessed the flowering of monastic life as did Rome.’ The sources reveal a count of nearly a hundred monasteries founded in the City of Rome between the fifth and the tenth centuries. Forty-nine of these appear in the roll-call of Roman ecclesiastical institutions included in the Liber Pontificalis entry for Leo III in 806/7 – suggesting that eighth-century Rome, no less than Skellig Michael off the south-west coast of Ireland or S. Vincenzo al Volturno in the Abruzzi, played a part in the heroic era of monastic foundation in early medieval Europe. And yet, having enumerated the Roman monasteries of this period, there seems to be very little else we can say about them. Thus Guy Ferrari's (still indispensable) Early Roman Monasteries: Notes towards a History of Monastic Observance in Rome takes its title advisedly, as a warning to avoid disappointment on the part of those expecting a sustained analysis of the city's monastic life. The Notes are set out as a series of institutional biographies, in alphabetical order – but what Ferrari in fact shows is the impossibility of rendering the papal biographies of the Liber Pontificalis, and the evidence from other sundry documentary or epigraphic sources, into a coherent and satisfying fulfilment of his own scheme. In the fifty years since the publication of Early Roman Monasteries, no one has attempted to write up Ferrari's Notes.

On the Monte Celio, the transformation of Rome from late ancient to medieval city appears to unfold before our eyes. A short walk from the Colosseum takes one to the Clivus Scauri, an exquisitely preserved Roman street running up the hill, and to the formidable redoubt of Christian monuments built around it. To one side, the monastery of S. Gregorio, founded by Gregory the Great on his own property, and its satellite chapels. Immediately adjacent is the so-called ‘bibliotheca Agapeti’, a reminder of the Christian university planned by Pope Agapetus. Behind this cluster, on the eastern slope of the hill, is the Lateran Palace, commissioned by the emperor Constantine in the fourth century, and the regular residence of popes from the seventh. Archaeologists are now persuaded that Constantine's palatial development was accompanied by interest in the neighbourhood from the most powerful private investors in the city, the Anicians. By 400, the dynasty was well established there, having converted shops and houses into a massive residential complex – the direct or indirect parent of the papal stronghold that took shape in the sixth century.

The shift from private mansion to ecclesiastical redoubt seems still more powerfully enacted on the other side of the Clivus Scauri, in the church of SS. Giovanni e Paolo. According to their passio, John and Paul were executed in the reign of Julian the Apostate (361–363), and buried in their house; under the sponsorship of a senator Byzantius and his son Pammachius, the house became a church.