The Groma is a surveying instrument utilized by the Roman Agrimensors or Geometres to align the boundaries of fields and general areas. It was used to set out the original land divisions as well as check their veracity after years of farming and thus to resolve land boundary disputes. It is well documented, but hard to establish in practice as a physical object. Thus the papers so far written are perhaps lacking in practical assessment of its utilisation in the field. This paper analyses the evidence by practical application, and assesses the likely construction.

The text is 4 A4 pages and 3 full colour A4 diagrams.

June 2010
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From the centuries BCE, Cosmographers, Geometres and historical authors bequeathed to us a variety of facts appertaining to their known world, the oikoumene. Most of the measurements were obtained by the traditional methods, “day’s travel” or “day’s sailing”. There existed though trained surveyors, “Bematists” who by accurate pacing measured progress and “Cord Stretchers”, whereby precise measures were obtained.
Herodotus tells of expeditions and maps extant in the 7th to 5th centuries BCE, and Hecataeus of Miletus, C550-476BCE, was able to write his books entitled “Ges Periodos”, “travels around the earth”, as a Periplus.
Various other Cosmographers, Geometres and historical authors added their own text, or recycled previous author’s work, to add to the corpus of information accumulating. This was mainly gathered at Alexandria after the formation of the Ptolemaic Dynasty in Egypt.
The collation of many facts led to perhaps the first of the scientific world measures, that of Eratosthenes, with his famous method and cosmography.
Then Rome became the all powerful state, absorbing Greek “Gnous”, and by 60 BCE dominated the Mediterranean lands. Julius Caesar then consolidated the Roman Empire.
But that Empire was perhaps intangible to many Romans, being only names on parchment. Thus Julius Caesar instructed a formal World Survey, choosing four Greek Geometres for the task and gave each a cardinal segment. But, having given those instructions he was infamously slain in 44BCE, and his adopted son, now Augustus Caesar, completed the task and by 6BCE a map was displayed in Rome.
Then soon after the commencement of our common era, Strabo, c15CE, wrote his “Geography”, based upon the work of Eratosthenes, but added his own travels and observations. Pliny the Elder, c75CE, wrote his “Natural History”, which was based upon the Roman Survey and its aftermath, and in c100CE, Marinus the Tyrian wrote his “Geography”. That text is the basis of the work by Claudius Ptolemy, his “Geographike Hyphegesis”, c150CE, the only extant cosmography now available from that period and used by most cartographic historians.
Then slowly but surely a new and possibly intellectual sect appears, Christians. The Roman Empire wains and is defeated by Odoacer in 476CE, but by 391CE Rome had already accepted Christianity as the state religion. Thus we can observe one state ruled by a Caesar being supplanted by a nebulous state, but ruled by a Pope and taking on the trappings of Roman technology, using their survey methods by studying the texts of the Agrimensores and Geometres. Later the formalisation of Monastic establishments into one design followed the Roman Army principle of identical layouts, such that peripatetic soldiers and the monks could locate their place easily in a new establishment.
Thus the Roman World Survey which had gathered in extant knowledge, then amplified it with new research, enabled following generations to progress both with formal surveying and cartographically.

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October 2011
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