- The Upright: a long pole with a metal point on the bottom for driving it into the ground.
- The Rostro: an arm that extended horizontally from the top, then angled upward, designed to swivel where it attached to the Upright.
- The Groma: a cross of four equal-length arms, with its center at the top-point of the Rostro. From the end of each arm, an equal length plumb line descended.
- The Marker Peg: a plumb line that descended from the center of the Groma's cross-piece all the way to the ground.
Who used the groma? Land surveyors, or as they were called in Latin, Agrimensores (from ager, "field" and mensura, "measure). Which brings me to the Corpus Agrimensorum Romanorum ("The Work of Roman Surveyors"), considered the earliest scientific or technical manuscript that exists, from a time (the 5th-6th centuries) when most documents were about religion or literature (or politics). The page seen here is from the section on laying out a house as opposed to a settlement. One picture is of the house, and one is of the property lines around it.
A 1554 edition of the Corpus added illustrations to the text with grid-lines to show the accuracy of the process. A few examples of its pages and illustrations can be seen here. And if you are interested in robots, you might get a chuckle from this after today's post.