Insights from a tribological analysis of the tribulum

Abstract

Since the 1980s, “strange” microwear traces were found to occur on flint blades from sites in the Near East from the late Neolithic and occurring in great abundance by the Early Bronze Age. Although these were considered by archaeologists to be sickles because they had visible gloss on their edges, their use-traces could not be reproduced in harvesting experiments carried out in the field. Subsequently, several lines of evidence were used to study the blades, including not only direct observation of microscopic wear traces, but also Near Eastern cuneiform texts from the third and second millennium BC describing agricultural instruments and analogy with ethnographic and experimental reference material. We found that these tools and their traces best matched traces on flint used to arm the underside of a tribulum (threshing sledge) for threshing grain and cutting straw. We built a replica of the tribulum described in cuneiform texts from the Bronze Age, using copies of the Bronze Age blades, and used this instrument in experiments. The publication of S. A. Semenov's work concerning traceology of ancient implements [S.A. Semenov, Prehistoric Technology (M.W. Thompson, Trans.), Cory, Adams and Mackay, London, 1964] awakened considerable interest in the possibilities of directly inferring tool function from the microscopic traces left by use on ancient implements. However, the goal and purpose of microwear studies is to reconstruct, as completely as possible, the economic activities of prehistoric groups, requiring a methodology that embraces all aspects relevant to the interpretation of microwear traces [L. Keeley, The methodology of microwear analysis: a comment on Nance. American Antiquity 39 (1974) 126–128]. In this study, we apply the science of tribology, which studies the friction and the wear of solid bodies in contact, to the threshing sledge and its blades. Tribological analysis of the tribulum has thus far provided new explanations for the formation of traces of wear on flint inserts in threshing sledges, while also revealing features on a far smaller scale, involving the role of a film deposit. We determine the mechanisms by which the tribulum threshes grain, and, particularly, fine-cuts straw from the sheaves of cereal laid on the threshing floor. The superior functioning of the tribulum compared to other methods of threshing and cutting straw is due to its great control of the rheology–the deformation and flow–of the straw layer on the threshing floor. The study lead to insights as to the mastery, of what may be considered today to be complex tribological principles, in the Bronze Age and probably beginning in the Late Neolithic [P.C. Anderson, Observations on the threshing sledge and its products in ancient and present-day Mesopotamia, in: P.C. Anderson, L.S. Cummings, T.K. Schippers, B. Simonel, (Eds.), Le traitement des récoltes: un regard sur la diversité du Néolithique au présent, ADPCA, Antibes, 2003, pp. 417–438].