Land cover and use-history of large empty spaces at fortified Iron Age hilltop sites; a case study from La Terrasse, Bibracte oppidum

Vegetation History and Archaeobotany https://doi.org/10.1007/s00334-023-00934-0 ORIGINAL ARTICLE Land cover and use‑history of large empty spaces at fortified Iron Age hilltop sites; a case study from La Terrasse, Bibracte oppidum Mária Hajnalová1 · Petra Goláňová2 · Eva Jamrichová3 Romana Kočárová7 · Patrik G. Flammer8 · Ákos Pető9 · Libor Petr4 · Markéta Fránková3 · Peter Barta5,6 · Received: 21 January 2023 / Accepted: 20 April 2023 © The Author(s) 2023 Abstract The research of Iron Age oppida and hillforts plays a significant role in understanding the urbanisation processes throughout the European continent. The habitation and built-up areas have always been in the limelight of both traditional and environmental archaeological research. However, at many oppida, there were also large, unoccupied empty spaces. As they are crucial for understanding these settlements’ internal organisation, their functions are debated. Here we aim to demonstrate that seldom studied archaeobotanical archives preserve information on their use-history. By implementing a multiproxy approach, we seek to answer questions on the development, land use and vegetation history of one important open space at Bibracte oppidum on Mont Beuvray. Through the correlation of pollen, phytoliths, diatoms, charcoal, seeds, and parasites with radiocarbon dating we collected evidence of archaeologically otherwise untraceable human activities and detected a much more complicated history of the studied area. We show that it was repeatedly used in the last eight millennia and was never farmed or built up. During the phases of its most intensive exploitation in the Late Iron Age (La Tène) and Early Middle Ages (Merovingian) periods, it was kept as grassland. Our research lays down the foundation for the wider implementation of archaeobotany into projects that aim to clarify the uses and functions of enigmatic large open spaces, not only from the Iron Age but also from other periods. Keywords Plant macroremains · Multiproxy analysis · Late iron age · Empty spaces · Oppida · Bibracte Introduction This article presents the results of a palaeoenvironmental study that aims at the reconstruction of the vegetation cover and use-history of non-built-up, empty and relatively large Communicated by C. C. Bakels. * Mária Hajnalová 1 2 Department of Archaeology, Faculty of Arts, Constantine the Philosopher University, Hodžova 1, 94901 Nitra, Slovak Republic Department of Archaeology and Museology, Faculty of Arts, Masaryk University, Arna Nováka 1/1, 602 00 Brno, Czech Republic 3 Department of Paleoecology, Institute of Botany of the Czech Academy of Sciences, Lidická 25/27, 602 00 Brno, Czech Republic 4 Department of Botany and Zoology, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic 5 Nuclear Physics Institute, Czech Academy of Sciences, Řež 130, 250 68 Řež, Czech Republic 6 Bratislava City Museum, Radničná 1, 815 18 Bratislava, Slovak Republic 7 Independent Researcher, Kokořov 2, PSČ 33501 Žinkovy, Czech Republic 8 Department of Zoology, University of Oxford, Woodstock Rd, Oxford OX2 6AD, UK 9 Department of Nature Conservation and Landscape Management, Institute for Wildlife Management and Nature Conservation, Hungarian University of Agriculture and Life Sciences, Páter Károly u. 1, Gödöllő 2100, Hungary 13 Vol.:(0123456789) Vegetation History and Archaeobotany areas that occur within the Late Iron Age urbanised enclosed sites—oppida and hillforts. It is based on the combination and correlation of five different archaeobotanical proxies— pollen, phytoliths, diatoms, charcoal, and seeds—with analyses of parasites and archaeological stratigraphy obtained from one of the large open spaces at the oppidum Bibracte in central France. Archaeological traces of populations living during the Late Iron Age (5th–1st century bc) in temperate Europe from the Atlantic to the Carpathian Basin are assigned to the La Tène culture that bears many common features but can differ considerably regionally. These Late Iron Age societies, traditionally connected with the Celts or Gauls, known from ancient written sources, witnessed profound social, political and cultural transformations. One of them was connected to urbanisation and in the 2nd–1st century bc resulted in the construction of oppida. These large, fortified ‘Celtic towns’, that occur in the vast territory of transalpine Europe stretching from the British Isles to the Danube Bend, fulfilled complex functions including roles of political, religious, and economic centres. Large-scale excavations conducted in many oppida open insights into the general urbanistic organization of the site and use of space within it. They almost exclusively focus on the originally built-up areas. Yet, unbuilt areas within these sites, which appeared as empty spaces for prolonged periods may have played an important role in the oppida urbanism and were possibly created just as deliberately as the architecture itself (Smith 2008). The relatively small areas, up to hundreds of square metres, surrounded by buildings and sometimes paved, are generally identified as public spaces (‘squares’). Less clear is the function of large empty spaces that cover up to several hundred or thousand square metres and usually separate (or connect) different residential zones and/or line the fortifications. The debate on their function has taken place for over a decade (cf. Fichtl 2005). Hypotheses on their usage as fields, pastures, spaces for social gathering, markets, refuge, and spare land for urban development, or various combinations thereof, have been put forward (Metzler et al. 2016; Winger 2016; Moore 2017; von Nicolai 2017). Most of these roles and functions are drawn from theoretical frameworks, ethnography, history, or sociology but are seldom tested and supported through bio-, geo- or other archaeological evidence. The exception is the use of open spaces for farming. Based on the distribution of rare finds of farming implements and scattered reworked pottery fragments, recovered from the top-soil horizons during prospections or excavations it was argued that during the life of Iron Age oppida (or hillforts) the open spaces were used as arable land or as grazing grounds (Křivánek et al. 2013; Winger 2016; Knopf et al. 2000). Further, a system of channels delimiting rectangular plots and plant macroremains (seed) assemblages from their fills, which differed 13 from assemblages from habitation areas, were interpreted as direct evidence that the open space at the lowland oppidum at Manching was used for arable farming (Küster 1992). Pollen data originating from waterbodies such as lakes or cisterns situated directly in some of the hilltop oppida/hillforts were also used for reconstruction of land management and vegetation cover. However, the sources of pollen might originate from further afield (cf. oppidum Corent, Ledger et al. 2015) or might date from the (...truncated)