Thunder ( lat. Groma, gruma ) - measuring and geodetic tools of ancient Roman agrimensor .
Title
The name probably derives from the Greek word γνώμων in the meaning of “square”, which is distorted in Etruscan. In Latin, it was also called ferramentum (literally "iron device", by the material of the main part), tetrans and stella ("star", on the upper part).
Device and Application
engraving by Karl Stefan and Johann Liebhalt; Strasbourg, 1579
It consists of a long vertical pole, to the top of which is attached a cross-member (or cross) on a turning mechanism; it can move horizontally. A plumb line is attached to each end of the crossmember. Having established thunder in the ground, agrimensor fixed the cross according to the cardinal points, focusing on the position of the sun and the plumb lines. The assistant departed a hundred steps and laid the load, indicating the direction, in accordance with the instructions of the agrimensor. So marked the axis of the future markup, corresponding to the cardinal points.
Thunder was originally used in the Etruscan ritual of founding cities, then by land surveyors in Rome, in particular, when measuring the land for the construction of a city or a Roman camp . The center of such a camp or forum in the city, the intersection of the cardo and decumanus , was also called “Thunder,” because the right angle of this intersection was originally drawn by the agrimensor with the help of thunder.
Several thunder were discovered during excavations, a detailed reconstruction of their device is possible.
Literature
- Cesare Polli, Marco Ceccarelli, Michela Cigola. The groma, the surveyor cross and the chorobates. La Groma, Lo Squadro agrimensorio e il corobate. Note di approfondimento su progettazione e funzionalità di antiche strumentazioni [Drognare Idee Immagini. Anno XXII. n. 42/2011. Pp. 22-33.
- Jean Peyras. Le vocabulaire militaire des arpenteurs latins du Haut-Empire // Jean Peyras. Les vocabulaires techniques des arpenteurs romains // Actes du colloque international (Besançon, 19-21 septembre 2002). Vol. 993. Besançon, Institut des Sciences et Techniques de l'Antiquité. Coll. ISTA, 2006, chap. 1, pages 137-148.
- Klaus Grewe. Chorobat und Groma. Neue Gedanken zur Rekonstruktion und Handhabung der beiden wichtigsten Vermessungsgeräte antiker Ingenieure // Bonner Jahrbücher. Bd. 209, 2009. S. 109–128.
- Nikolaus Thurn. Die Geburt der Theorie aus dem Instrument. Über Bedienung und Bedeutung der antiken Instrumente Groma und Lyra. Fink, Paderborn UA 2008. ISBN 978-3-7705-4474-5 .