RRCAMP-10R Roman Gromatici, Roman Camp
The GROMA or Gruma was a Roman Surveying instrument. It comprised of 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.
They were stabilized on the high ground and pointed in the direction it was going to be used. The assistant would step back 100 steps and place a pole. The surveyor would tell the assistant where to move the pole, who would then set it down.
The groma surveying instrument may have originated in Mesopotamia or Greec before the 4th Century BC, and is believed to have been brought to Rome by the Etruscans.