The relative textual and archaeological invisibility of the 10th and 11th centuries at Rome is especially vexing for coming at a critical transitional period, just when the early medieval city began to metamorphose into the very different sort of place it became in the later Middle Ages. The later medieval city as it emerged from the 12th century on broke with its ancient roots in a number of ways. At least as late as the 9th century, upper-class residences like the ones in the Forum of Nerva retained a distinctly unfortified profile; though these houses were smaller and more compact than the aristocratic mansions of imperial Rome, they nonetheless prolonged a tradition of accessible, ‘civilian’ residential architecture that had continued unbroken for a thousand years. By the 12th century, however, Roman nobles lived in fortified compounds, complete with defensible outer walls and tall towers. As late as the 10th and 11th centuries, very few churches had bell towers, either; the soaring, graceful campanili attached to surviving medieval churches only proliferated in the 12th. In the 9th and 10th centuries, patches of settlement still extended across much of the intramural area.