MEASURING THE LAND IS AN ART ALMOST AS OLD AS HUMAN SETTLEMENT, and among ancient peoples the Romans were its masters. The voluminous surviving Roman literature on the subject pertains mostly to partitioning rural plots. However, by the mid-first century C.E. at least, the surveying techniques developed for that purpose were also being used to map the more convoluted and irregular landscapes of towns. The need for urban maps seems obvious today. They facilitate the design, construction, maintenance, and modification of the entire urban prospect and its infrastructure. They clarify legal status, and thus simplify revenue collection and adjudication of land disputes. They assist in keeping track of individuals and families; they help fire brigades and police do their jobs. For a census-driven urban bureaucracy such as Rome's, grounded in the identification and enrollment of a million people or more according to their property status, maps would seem not only warranted, but indispensable.

This commonsense proposition is not universally accepted, yet we are fortunate to have strong evidence supporting it. First and foremost, there is the Severan marble plan of the city. Probably a revision of a fire-damaged Flavian antecedent, it was affixed to a wall of the Templum Pacis around 203 C.E. or slightly later (see Fig. 49). About 10 percent of the original 1:246-scale planimetric map survives today in nearly 1,200 incised marble fragments fallen from the wall, which still stands, though entirely stripped of its accompanying enclosure and adornment (Fig. 86). An overpowering display of technical virtuosity, it is sometimes dismissed as a showpiece with purely rhetorical value like Agrippa's map of the known world in the Porticus Vipsania. Yet the use of maps for administrative purposes across the Roman world is well established. Vespasian's land cadasters at Orange, France, and a lost fragment of an aqueduct map from Rome marking private water concessions (Fig. 87), the second rendered schematically rather than planimetrically, were certainly derived from archival originals. Fragments of other marble maps survive, too, several on the same scale as the Severan plan and sometimes indicating the peripheral measurements of properties in Roman feet.