The Second Century CE Roman Watermills of Barbegal Unraveling

The second century CE Roman watermills of Barbegal Unraveling the enigma of one of the oldest industrial complexes Gül Sürmelihindi, Philippe Leveau, Christoph Spötl, Vincent Bernard, Cees W. Passchier To cite this version: Gül Sürmelihindi, Philippe Leveau, Christoph Spötl, Vincent Bernard, Cees W. Passchier. The second century CE Roman watermills of Barbegal Unraveling the enigma of one of the oldest industrial complexes. Science Advances , American Association for the Advancement of Science (AAAS), 2018, 4 (9), pp.eaar3620. 10.1126/sciadv.aar3620. hal-01881252 HAL Id: hal-01881252 https://hal-univ-rennes1.archives-ouvertes.fr/hal-01881252 Submitted on 19 Jul 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. SCIENCE ADVANCES | RESEARCH ARTICLE ANTHROPOLOGY Copyright © 2018 The Authors, some rights reserved; The second century CE Roman watermills of exclusive licensee American Association Barbegal: Unraveling the enigma of one of the for the Advancement of Science. No claim to oldest industrial complexes original U.S. Government Gül Sürmelihindi1, Philippe Leveau2, Christoph Spötl3, Vincent Bernard4, Cees W. Passchier1* Works. Distributed under a Creative Commons Attribution The second century CE Roman watermill complex of Barbegal, France, is regarded as one of the first industrial NonCommercial complexes in human history. The 16 water wheels are no longer extant as all woodwork has decayed. However, License 4.0 (CC BY-NC). carbonate deposits precipitated from water during operation of the mills forming casts on the woodwork. These casts are preserved in fragments and provide unique insights into the frequency of use and maintenance of the mills, and even into the structure of the water wheel chambers. Stable isotope time series of carbonate deposits reveal that the mill activity was regularly interrupted for several months. This strongly suggests that the mill complex was not used for a steady supply of flour to a major population center, as previously thought, but likely served to produce nonperishable hardtack for the nearby harbors. Downloaded from INTRODUCTION Today, nearly 80 years after the first excavation of the complex The Greco-Roman world has been presented by many scholars as (1937–1939), key questions still remain open: What was the desti- an example of a society that was stagnant in terms of technological nation of the large amount of flour produced by the mill complex? innovation and development, accrediting the idea that, although an How did it function and for how long was it in use? And did mill http://advances.sciencemag.org/ ancient invention, watermills were first used on an industrial scale complexes of this scale spread over the Roman Empire? These questions in medieval times (1–4). The scarcity of written sources on this subject have remained unsolved because the ruins are only fragmentary, in antiquity, for example, by Strabo, Vitruvius, Pliny, Palladius, and excavation records are incomplete (10), and only few other industrial Antipater (3), may have supported this view. Over the past decades, sites of comparable scale are known in the Roman Empire. Here, we however, numerous Roman mill sites have been discovered by show that novel laboratory techniques and interdisciplinary research archaeologists, and it has become clear that there was considerable can shed new light on these long-standing questions. innovation in Roman times, especially in the field of hydraulics Many Roman water supply systems were fed by karst springs with and the use of watermills from the first century CE onward (1, 5–9). a high content of calcium and bicarbonate. These ions are kept in A prominent, yet not widely known example of a technological solution by enhanced PCO2 (partial pressure of CO2) and associated masterpiece is preserved at Barbegal in southern France (Fig. 1, low pH values due to the passage of rainwater through the soil A and B), where a large water-powered grain mill complex was built before entering the karst system. When the water leaves the karst on July 19, 2019 in the second century CE (10–12). The Barbegal watermill complex spring, CO2 degasses and, as a consequence, calcium carbonate is the earliest and largest known industrial utilization of hydropower precipitates both naturally in the form of tufa and on artificial by an ancient society. The complex, composed of 16 watermills structures of water management systems. Because the rate of depo- (Fig. 1, C and D), has been described as “the greatest known con- sition is influenced by the temperature, the chemical composition, centration of mechanical power in the ancient world” (1, 5) and has and the flow rate of the water, the deposits form layers of different no equivalent either in the Roman world or in Asian civilizations, crystal structure and chemical and isotopic composition, creating a although both are known for their achievements in other fields of natural archive of past environmental conditions. Carbonate deposits hydraulic engineering (6, 10, 13). Originally, it was believed that from water supply systems fed by karst springs therefore not only the mills of Barbegal were built at the end of the third century CE, are an established paleoenvironmental archive but also hold high when Arles was the residence of the Emperor Constantine, for the promise as an archaeological resource. These deposits store infor- production of flour for the imperial administration, the army, and mation on water temperature, discharge, and composition, as well as the city (10). The mills were previously used to illustrate a profound on structural changes to the water systems, both natural (for example, social change: With Christianization, the end of slavery liberated damage by an earthquake or flooding) and artificial (for example, the inventive capacities of engineers and favored the use of natural repair work of channels) (14–16). energy, in this case, hydropower, to produce flour. However, excava- In the collection of the Archaeological Museum of Arles, we found tions in the early 1990s led to the abandonment of this hypothesis 142 fragments of carbonate deposits that stem from the first Barbegal (11) and recognized Barbegal as a unique, early climax of techno- excavations performed in the 1930s. These deposits had formed logical development. on (now decayed) wooden parts of the mills that had been in direct contact with flowing water. We examined these carbonate frag- 1Department of Earth Sciences, Johannes Gutenberg University, 55128 Mainz, ments macroscopically and microscopically and by means of sta- Germany. 2Aix-Marseille Université, CNRS, Centre Camille Jullian, UMR 7299, ble isotope analysis. The microstratigraphy of the individual 13094, Aix-en-Provence, France. 3Institute of Geology, University of Innsbruck, Innrain 4 specimens provides unique new insights into the use of the mills, 52, 6020 Innsbruck, Austria. Université Rennes 1, CNRS, UMR 6566, CReAAH, Rennes, France. their maintenance, and the ultimate destruction of this industrial *Corresponding author. Email: [email protected] complex. Sürmelihindi et al., Sci. Adv. 2018; 4 : eaar3620 5 September 2018 1 of 8 SCIENCE ADVANCES | RESEARCH ARTICLE Downloaded from http://advances.sciencemag.org/ Fig. 1. Location and reconstruction of the Barbegal watermill complex. (A) Overview map. k, karst springs. (B) Detailed map of the small red rectangle in (A). The southern aqueduct (light blue) fed into the mill complex. Blue arrows indicate flow directions. Dotted lines: contour lines (m). (C) Proposed reconstruction of the complex, consisting of two parallel rows of watermills in open-air conditions, built on a hillslope. (D) Alternative reconstruction proposed in this study, where the watermills were enclosed within buildings. RESULTS that fed the water to the mill (Fig. 2, A to D) and deposits that had Site description formed on the wooden parts of the actual water wheels (examples The Barbegal mill complex (43°43.28′N, 004°43.17′E) was situated shown in Fig. 2, E and F). Calcite crystals grew perpendicularly to the approximately 8 km northeast of the Roman city of Arelate, the surface of the substrate. The deposits growing in the millrun flumes on July 19, 2019 modern city of Arles (Fig. 1, A and B). The complex consisted of formed a U-shaped profile. When the wood had decayed or had been two parallel rows of eight aligned watermills, fed by an aqueduct removed, the deposits broke preferentially into planar fragments and with housings covering the grain mills (Fig. 1, C and D). The along 45° angles, allowing the identification and reassembly of in- mills had an estimated production capacity of 25 metric tons of dividual flume fragments (Fig. 2, C and D). The flumes were 30 to flour per day, enough to feed a population of at least 27,000 people 33 cm wide with sides of 17 to 22 cm high. The wood imprints bear (5). The 9-km-long mill aqueduct collected water from several small evidence of resinous logs sawn tangentially into planks. Regular karst springs, located along the southern side of the Alpilles

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