The Acheulean technology represents a significant stage in the development of Human technology, appearing in East Africa around two million years ago, and associated with the first major spread of Hominins out of Africa on the Middle Pleistocene. The oldest known Acheulean tools from South Asia were deposited in Tamil Nadu about 1.5 million years ago, which the youngest come from the Middle Son Valley of Central India, and are between 140 000 and 100 000 years old. While many Middle Pleistocene settlements in India appear to have been occupied for relatively as people moved about in response to a changing climate and landscape, the Son Valley appears to have provided a stable environment facilitating a long period of Hominin inhabitation, and is thought likely to have been a significant centre for the distribution of Hominin populations into other parts of South Asia, with a large number of sites discovered in the middle and lower parts of the valley. The upper reaches of the Son Valley, however, have not been extensively studied by archaeologists.
In a paper published in the journal Antiquity on 20 February 2025, Hemant Kumar Vaishnav and Bora Janardhana, of the Department of Ancient Indian History, Culture and Archaeology at the Indira Gandhi National Tribal University, and Deepak Kumar Jha of the Department of Coevolution of Land Use and Urbanisation at the Max Planck Institute of Geoanthropology, and the School of Archaeology at the University of the Philippines Diliman, present the results of a survey of the Upper Son Valley for Acheulean stone tools.
Vaishnav et al. surveyed the upper reaches of the Son River, between Amarkantak Hill in Chhattisgarh State, where the river arises, and Lake Bansagar in Madhya Pradesh, on foot in 2022 and 2023, examining the river channel, terrain, cliff sections, gullies and tributaries. This process led to the discovery of eight new Acheulean sites, and 1348 individual lithic artefacts.
Handaxes were the most common tools, particularly at the Mahuda Site on the left bank of the river. Cleavers were present at most sites, though not in great numbers. These tools were made by the bifacial shaping (shaping of a tool by removing pieces from both sides) of blanks made from medium-or-large rock flakes. Two sites, Chilhari and Semarpakha, produced tools made using the more-advanced Levallois technique, which involves forming a striking platform at one end of a stone tool, then trimming the core's edges by flaking off pieces around the outline of the intended lithic flake, prior to separating the tool with a final blow.
Characterisation of handaxes and their raw materials in the Upper Son Valley: (a) & (b) chert; (c) quartz; (d)–(f) quartzite; (g) sandstone Vaishnav et al. (2025).Tools wre made from quartzite, chert, and quartz, with fine grained quartzite, abundant in the region, being the most commonly used material at all sites except Chilhari, where the majority of tools were made from a course sandstone obtained locally.
The most common items were flakes, comprising 65.8% of the total, followed by handaxes (14.8%), cleavers (4.3%), choppers (0.5%), retouched tools (7.8%) and cores (6.3%). Notably, the Silpahari site produced 47 handaxes but no cleavers, which may relate to local landscape usage.
Characterisation of cleavers and their raw materials in the Upper Son Valley: (a)–(d) quartzite; (e) & (f) chert; (g) sandstone; (h) quartz. Vaishnav et al. (2025).Material from the Chichgohna and Silpahari sites showed little signs of wear, that from Semarpakha was highly worn and weathered, and material from other sites showed variable levels of wear. This probably reflects energy levels in these environments (higher energy environments tend to have fast moving water with strong currents).
The eight new sites in the Upper Son Valley support the long-term usage of the valley by Hominins in the Middle Pleistocene, with the tools interpreted in being Early to Late Acheulean in age, with the latest site being at Silpahari, where the handaxes have become smaller and slimmer, and cleavers are absent, interpretted as signs of a Late Acheulean phase in South Asia.
The high energy levels which many of the tools were deposited in imply a fast-flowing river system, which in turn implies abundant water, which would have made for a good environment for Hominins in the sometimes-arid Pleistocene. The tools were well made, using the best locally available rock, suggesting these Hominins had a good understanding of both toolmaking and their environment.
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