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The ''Groma'' or ''gruma'' was a Roman surveying instrument.〔Cesare Rossi, Marco Ceccarelli, Michela Cigola, The groma, the surveyor's cross and the chorobates. In-depht notes on the design of the old instruments and their use. La Groma, lo Squadro agrimensorio e il corobate. Note di approfondimento su progettazione e funzionalità di antiche strumentazioni, in Disegnare Idee Immagini, anno XXII n. 42/2011; pp. 22-33. ISBN 978-88-492-2248-7, ISSN IT 1123-924〕 It comprised 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. The same name was given to: * the center of any new military camp, i.e. the point from which was traced the regular grid by using the ''groma'' instrument * the center of a new town, from which the gromatici (surveyors) began to lay out cardo and decumanus grid, with a plough and a pair of oxen The groma surveying instrument may have originated from Mesopotamia, and may have been imported by the Greeks in the 4th century BC. Subsequently, it was brought to Rome by the Etruscans and named cranema or ferramentum. ==Notes== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Groma surveying」の詳細全文を読む スポンサード リンク
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