In 846, Muslim Arabs unsuccessfully stormed the city's walls, but managed to loot St. Peter's and St. Paul's basilica, both outside the city wall. After the decay of Carolingian power, Rome fell prey to feudal chaos: several noble families fought against the pope, the emperor, and each other. These were the times of Theodora and her daughter Marozia, concubines and mothers of several popes, and of Crescentius, a powerful feudal lord, who fought against the Emperors Otto II and Otto III. The scandals of this period forced the papacy to reform itself: the election of the pope was reserved to the cardinals, and reform of the clergy was attempted. The driving force behind this renewal was the monk Ildebrando da Soana, who once elected pope under the name of Gregory VII became involved into the Investiture Controversy against Emperor Henry IV. Subsequently, Rome was sacked and burned by the Normans under Robert Guiscard who had entered the city in support of the Pope, then besieged in Castel Sant'Angelo.