WHEN THE BYZANTINE EMPIRE CEDED CONTROL OVER THE PAPACY IN 752, the Church, now protected by the Franks, became a vassal of the Carolingian dynasty. Charlemagne, first as king (768–814) and then as Holy Roman Emperor (800–814), and Popes Hadrian I and Leo III joined in a relatively stable alliance. Meanwhile, ties between the Church and the Byzantine rulers unraveled in the mid-ninth century as threats from outside invaders such as the Lombards and Saracens increased. The Church and the Holy Roman Empire coexisted uneasily for more than five centuries, with the emperor most often dominating. The growing Roman noble class, itself divided into ruthless factions, sometimes supported the pope and at other times the emperor.

This led to several important changes. The continued Saracen peril on the seas spelled the end of the port facilities at Ostia and Portus, and their abandonment resulted in some new, smaller river ports to augment those already within the city. The exposed countryside contained treasures, both material and spiritual, that had to be moved within the wall for safekeeping or given their own local protection. Relics of martyrs and other Christians, hitherto inviolable where they lay, were now dug up and taken into the city, where they were distributed among the churches. At the same time, the great shrines were fortified. The fort of Johannipolis around the complex of S. Paolo and the Leonine Walls of the Borgo were the work of the ninth century. In the Roman countryside both the castle and the fortified village (both called castellum) had become common. The population shifted markedly to new defensible centers and the domus cultae broke up. The once tightly administered papal domain, a vast landholding operation strapped to the Lateran, splintered into fragments ruled by individual churches, monasteries, and increasingly the rising noble families. The same pattern of breaking up large units into smaller governable – that is, defensible – elements transformed the urban landscape as these families, for protection, engaged their own private gangs for open warfare in the streets.

But by the early tenth century one powerful family – the Tuscolani from ancient Tusculum southeast of Rome – effectively seized Rome and took control of the Church. We first hear of them in the person of Theophylact I (d. 924/5), count of Tusculum.