During the first half of the 4th century, anonymous authors compiled a pair of very similar catalogs of Roman buildings and landmarks, the Notitia and the Curiosum urbis Romae regionum XIIII, the “Description” (Notitia) and “Gazetteer (Curiosum) of the fourteen regions of the city of Rome.” Updated at least as late as the year 357, they listed noteworthy features of each of the city’s fourteen regions, the administrative subdivisions, like Paris’s arrondissements or London’s boroughs, that had been introduced by Augustus in 7 BC (Fig. 1.1). The two Regionary Catalogs, as they are now called, are the most comprehensive resource we have for the names and places constitutive of Rome’s urban fabric at the end of antiquity. For some areas, they are graphically supplemented by the surviving fragments of the Severan Marble Plan, a gigantic 1:240 scale map of Rome carved circa AD 203 into marble slabs mounted on a wall in the Forum of Peace (Fig. 1.2).