Ancient measurement tools
Article taken from "Backsights" Magazine published by Surveyors Historical Society
EGYPTIAN SURVEYING TOOLS
by Mary M. Root
Four thousand years ago, the concepts of math were basic, yet the Egyptians were able to achieve wonders. They used the predecessors of modern surveying instruments to engineer many feats, from canals to pyramids. An ancient Egyptian survey crew used measuring ropes, plumb bobs, sighting instruments, and leveling instruments.
The ancient Egyptian measuring rope (the old term for "surveyors" was "harpedonaptae" or rope-stretchers) was treated to hold its length. It was stretched taut between stakes and then rubbed with a mixture of beeswax and resin. Some of the ropes depicted in hieroglyph were graduated by knots tied at intervals. Accuracy was creditable, according to a 1909 triangulation survey that tied some original boundary stones. The Egyptian crews set the stones to divide the fertile Nile delta, and the "rope" was indispensable for measuring the distances.
Plumb bobs were appreciated for their ability to furnish a true vertical line. The Egyptians employed plumb tools in their sighting and leveling instruments, and as a way to continue distances vertically. They exploited all the possibilities of the bob, using it for astronomy, navigation, surveying, and building. It was their "workhorse" tool.
The sighting instruments were the "merchet" and the "groma". The merchet was a staff with a wide notched top. The notch was a long slit through which the instrument operator aligned a fixed plumb-line and the "rope-men". This enabled them to measure long lines effectively. The groma was a right-angle device designed for laying out fields, much like the surveyor's cross of more recent times. Of the two, the merchet was more accurate, and it was probably used to survey the pyramids.
Though nothing is known of the long-distance leveling devices, two different short-distance types were used to build the pyramids. The first was a water level. The bedrock was networked with narrow trenches, then filled with water. The waterline was marked on all the trench walls, the protrusions cut down, and the trenches re-filled with stone to create a level base. The second type of level was an A-frame with a plumb bob suspended from the apex. Since the Egyptians understood the isosceles triangle, stones could be cut and chiseled square, and mortared into place using this instrument.
Research continues to turn up new evidence of surveying in ancient Egypt. There are but a few papyri, hierglyphi, and actual artifacts documenting the surveyors and builders of their world. But to appreciate the symmetry of the Cheops pyramid, and to note that its north/south axis is only 03' 06" to the west of true north, means to today's surveyor that the Pharaoh wasn't wasting his money on his surveying bills. The surveyor's tools of the trade had come through.