Measuring the World

The following text appears on banner no. 5 in the exhibition space.

The Corpus Agrimensorum Romanorum, displayed here in facsimiles of a sixth- century manuscript and in its earliest printed edition of 1554, is a collection of instruction manuals on land survey devoted to the Roman techniques of dividing, measuring, and recording landholdings.

Surveying did not originate in Rome: as early as the second millennium bce, Babylonian cuneiform tablets attest to the application of arithmetic and geometric principles in solving problems related to the calculation of plots of land. In pharaonic Egypt, surveying techniques were extensively used to re-establish private boundaries following the annual floods of the Nile and for large-scale construction projects. In the sixth century bce, the Egyptian fundamentals of geometry and surveying were acquired by Greek philosophers interested in abstract theories that would explain the size and shape of the Earth. The third century bce saw the birth of Euclidean geometry (still the basis for geometry in today’s school’s curriculum) and the invention of the dioptra, a sighting tube that measured both the horizontal and the vertical planes, and allowed for more precise measurements and drawings of terrains.

This knowledge was eventually transmitted to Rome. Roman surveyors further developed it by employing new surveying instruments, primarily the groma and the libra, both of which were possibly of native Italian origin. The groma was a pole carrying a flat cross with a plumb bob hanging from each arm that allowed a surveyor to measure and draw straight lines and right angles, while the libra was an instrument used for vertical measurements.

Surveying developed in Rome in response to the practical issue of land taxation, and professional surveyors attended to all aspects of the craft. Chorographoi (cartographers) measured and drew large-scale areas, while agrimensores plotted agricultural fields and laid out rectangular grids to divide the cultivatable lands based on the centuria, a unit of about 120 acres. Mensores (measurers) followed the army to provide technical support during military campaigns, and libratores oversaw the construction of roads, aqueducts, irrigation systems, and navigable channels.

Roman surveyors were also directly involved in the planning of new settlements. Since the late Republican period (second–first century bce), colonies had been established for veterans in newly conquered regions. In the creation of a new town, the mensores chose the optimal location, set up the main axes and secondary road system, and divided the space inside the walls into plots. Additionally, they entered the details of each parcel in the local cadastral (public) records and sent copies, possibly engraved on bronze tablets, to the Tabularium, the record office in Rome situated within the Roman Forum. These records were used as official evidence in fiscal and tax disputes, and agrimensores were consulted in legal arbitration regarding the boundaries of private lands or the equal distribution of water for irrigation.