Author: Multimedia Laboratory of the Istituto e Museo di Storia della Scienza, Florence
The surveyor's cross was used to geometrically divide plots of land. It was composed of a supporting rod, a rotating arm (called a rostro) and the groma, or cross-staff. The desired orientation was achieved by rotating the rostro. The groma, a wooden cross with iron fittings, was on top of the rotating arm. From the extremities of the cross hung two pairs of plumb-lines. The projection on the earth of the four lines determined the coordinates of orientation, which were traced into exact dividing lines using aligned stakes.