In 1882 the German scholar of Antiquities Dr. Oskar Seyffert published a dictionary that was tranlated into English under the title: The Dictionary of Classical Antiquities* [see note]. In it appears an entry under the rubric Agrimensores. I found Seyfferts research extremely informative and want to pass it along. For better understanding I inserted into his definition explantions taking from other entries of his dictionary.
Agrimensores. The Latin name for land-surveyors, otherwise called gromatici, from groma, their measuring instrument. This consisted of two dioptric rods crossing each other at right angles and fastened on an iron stand so as to turn horizontally; on the four arms stood four upright dioptrae (sights), with threads stretched across the holes, and in taking observations the threads of two opposite dioptrae had to cover each other. The measuring was done on the same principle as the marking-out of a templum by the Augurs.
Templum was the Roman term for a space to be occupied by a temple, and marked out according to a certain fixed procedure. Its ground plan was a square or rectangle, its front, according to strict Roman custom, faced toward the west, so that anyone entering the temple had his face turned towards the east.
The Augurs consisted of four Patricians and five Plebeians appointed by the State. During the republic they were called in on all those occasions on which the State had to assure itself of the approval of the gods. The survey started by drawing two lines in the center of a piece of land, the lines intersecting at right angles, one from north to south (cardo maximus), the other from east to west (decumanus maximus). Further division of the ground was affected by parallels to these lines (limites).
It was not until the imperial period that land surveying became a separate profession. The surveyors were prepared in special schools and appointed by the State, both for quarter-master duty in camp and for measurements under Government. Surveyors decided as judges in fixing boundaries, and were consulted as specialists in disputes affecting land. Thus a literature arose, half mathematical, half legal, the remains of which extend over the first six centuries A.D. The earliest of these gromatici, or writers on land-measurement, is Frontinus.
Sextus Iulius Frontinus was born about 40 A.D. In 97 A.D. he was appointed to the important office of superintendent of the aqueducts. Under Trajan he was made an augur. Amongst his surviving works are selections from a treatise on land-surveying in two books, written under Domitian (emperor 81 96 A.D.) and dealing more with the legal side of the subject. Frontinus died in about 103 or 104 A.D., much esteemed by his contemporaries.
This ends the information provided by Seyffert. During the exavations of the ruins of Pompeii parts of a Roman groma were found. This particular instrument was not equipped with the dioptrae described by Seyffert, but instead required the use of four plumb bobs, one of each to be hung from the four ends of the cross. The string of the plumb bobs served as sighting devices. As can be imagined, if the cross was not to small, sighting over two opposite plumb bobs was quite accurate. A right angle could be checked by rotating the groma 90 degrees and sighting the established points again. To set the instrument over an existing point required a plumb bob suspended from the center of the cross that was several inches offset from the supporting staff.
Elsewhere in his Dictionary, Seyffert gives us some interesting information about Terminus, the Roman god of boundaries, under whose special protection were the stones (termini) which marked the boundaries. The regulations respecting these stones and the religious customs and institutions connected with them went back to the time of Numa Pompilius, legendary king (715 673 B.C.) of early Rome. At the setting of such a stone every one living near the boundary assembled, and in their presence the hole prepared for the reception of the stone was watered with the blood of a sacrificial animal; incense, honey and wine were sprinkled over it, and a victim sacrificed. The stone, anointed and decked with garlands and ribbons, was then placed upon the smoldering bones and pressed into the earth. Whoever pulled up the stone was cursed, together with his cattle, and anyone might kill him with impunity and without being defiled by his [the stone pullers] blood. In later times the punishment of fines was instituted instead.
The festival of the Terminalia was celebrated in Rome and in the country on the 23rd of February. The neighbors on either side of the boundary gathered round the landmark, with their wives, children, and servants, and crowned it, each on his own side, with garlands, and offered cakes and bloodless sacrifices. Lastly the whole neighborhood joined in a general feast. A lamb was also sacrificed in the grove of Terminus, which was six Roman miles from Rome, near the ancient border of the town of Laurentum. On the Capitoline Hill there was a stone dedicated to Terminus, which had originally stood in the open air, but when the temple of Jupiter Optimus Maximus was founded it was inclosed within the building, as the augurs would not allow it to be removed.
This writer remembers reading somewhere that Terminus was sometimes depicted as having neither arms nor legs in order to symbolize that he never moved from whatever place he occupied. Moving or destroying boundary marks (or neglecting their maintenance which is just as bad) is certainly not a modern invention, but it seems that in Antiquity there was less tolerance for this sort of endeavor. This writer notes always with great satisfaction that
* NOTE: Oskar Seiffert: The Dictionary of Classical Mythology, Religion, Literature and Art. Revised and Edited by Henry Nettleship and J. E. Sandys. GRAMERY BOOKS, New York, 1995