Groma surveying

The Groma or gruma was a Roman surveying instrument. It comprised a vertical staff with horizontal cross-pieces mounted at right angles on a bracket. Each cross piece had a plumb line hanging vertically at each end. It was used to survey straight lines and right angles, thence squares or rectangles. The same name was given to:

The groma surveying instrument may have originated from Mesopotamia, and may have been imported by the Greeks in the 4th century BC. Subsequently, it was brought to Rome by the Etruscans and named cranema or ferramentum.