Groma surveying



The Groma or gruma (altered from Greek gnomon γνόμων "indicator", possibly through Etruscan) was the principal Roman surveying instrument. It was composed of a vertical staff with horizontal cross pieces mounted on a bracket. Each cross piece had a plumb line and plumb bob hanging vertically. Its main use was to survey straight lines, squares, and rectangles. The same name was given to:
 * the center of any new military camp, ie the point from which was traced the regular grid by using the groma instrument
 * the center of a new town, from which the gromatici (surveyors) began to lay out cardo and decumanus grid, with a plough and a pair of oxen