Unraveling the Mystery of Spheroids: Prehistoric Artefacts Explained

In particular, the objects grouped under the terms polyhedra, spheroids and bolas (PSB) are enigmatic carved stone artifacts, the question of their function still remaining open today among prehistorians.

[Un article de The Conversation écrit par Julia Cabanès, Docteur-Archéologie, Ethnologie, Préhistoire, Muséum national d’histoire naturelle (MNHN)]

Produced during the last two million years throughout the Old World, these objects are very common in sites in Africa and Asia, but curiously, they are much rarer in Europe. In the literature, their definition depends mainly on their proximity to the sphere: they are objects carved on at least three faces, of angular morphology for polyhedra, faceted spherical for spheroids and perfectly spherical for bolas. Their sizes and weights are also very variable, ranging from a few grams to several kilos.

Despite their frequency in sites, these objects are very little studied and remain poorly understood. What were their roles in the daily lives of fossil hominins? Moreover, producing such objects is a complex process: why didn't hominins use simple spherical pebbles, instead of transforming pebbles into spheroids? Our recent study of 513 of these chipped stones, from nine Paleolithic sites in France and North Africa, has provided new elements to answer these questions.

A long-standing debate

First, let's take stock of existing studies and theories. It was in 1847 that Boucher de Perthes first described these types of objects, calling them “Celtic axes” when he discovered these stone balls in northern France. In the scientific literature, two main hypotheses propose that these objects are either tools shaped to perform a specific task, or on the contrary, final-phase cores, that is, cutting waste from which as many flakes as possible have been extracted, and where the flakes are the desired products.

For authors who consider that these objects fulfill a precise function, many see them as projectiles, based mainly on actualist reasoning, that is to say by comparison with objects used until recently: here, the boleador balls South American. These balls are spherical objects tied with rope, used by Native Americans and gauchos as throwing weapons. This comparison was so popular that the balls South American islands gave their names to the prehistoric bolas.

Other authors suggest that the spheroids are percussive tools, i.e. tools somewhat similar to hammers, but most of these studies are not based on any analysis. However, this hypothesis is supported by one of the only traceological analyses carried out on the spheroids, which, through the study of traces of use on the surface of the pieces from the Qesem site (Israel), concluded that these pieces were used to break bones in order to extract the marrow. Experiments also suggest that the spheroids from the Jonzac site (France) were used as percussive tools to carve flint tools. Finally, other authors propose – without prior analysis – that the spheroids would be club heads or pestles.

An unprecedented study of more than 500 artifacts

Theories about the functions of polyhedra and spheroids are therefore numerous, but rarely based on evidence. In our recent study, we analyzed 513 of these objects from nine sites in France and North Africa, dating from 1.8 million years to 169,000 years ago. We conducted a traceological analysis, aiming to document and interpret the sometimes microscopic traces on the surface of the objects. These traces provide clues on the methods of production and use of the pieces, but also on all the natural or accidental processes they may have undergone.

To interpret these traces, it is necessary to create repositories, i.e. banks of photographs of traces whose creation parameters are known (for example: the task performed, the number of movements). To create these repositories, we conduct experiments: it involves cutting replicas of spheroids and using them in different tasks (breaking bones, crushing plants) in order to document the evolution of the traces on their surface.

Thanks to these references, it is possible to interpret the traces on archaeological objects by comparison: are they due to production or use? To what use? In addition, the dimensions of an object, its weight and its ergonomics are all factors that can be considered by the cutter. The study of all these parameters allowed us to support our hypotheses.

Clues left during manufacturing

According to our results, polyhedra and spheroids are mainly produced in robust rocks, resistant to violent shocks, such as basalt or quartzite. On the contrary, less robust materials such as flint have been systematically avoided for two million years to produce these objects. However, according to our experiments, flint is adapted to manufacture such artifacts. Thus, flint seems to have been avoided rather for functional reasons: spheroids would be used in activities requiring resistance to violent shocks. This could also allow to discuss the rarity of spheroids in Northwestern Europe, where the sites are mainly located in sedimentary basins rich in flint and where the industry is very focused on the exploitation of this rock.

Our experiments showed that intense traces are created on the surface of the object during its production. In contrast, use produces little or no traces. Thus, contrary to what has been suggested in the literature, most of the traces on the surface of the spheroids are not due to intense use, but to their production. However, these objects could have been used without any trace of use being visible on the surface, as was the case in most of our experiments.

Why make these objects?

The rare traces of use that we have identified on the archaeological pieces could indicate percussion activities, such as bone breaking. The robustness of these objects – due to their raw materials and their robust edges – as well as their morphology which tends towards the sphere seem to be functional and/or ergonomic aspects sought by the hominins who produced these objects. Thus, most of the pieces in the corpus seem to have been shaped to carry out activities requiring resistance to violent shocks.

We did not observe any advantage in using a spheroid rather than a pebble. There is therefore a paradox between the complexity of the manufacturing process and the efficiency of these objects, which is equal to a simple pebble. In some cases, this paradox could indicate that spheroids would not be directly produced from pebbles, but that they would rather be the result of recycling objects produced on pebbles (cores, tools on pebbles).

According to our study, these objects represent a great diversity of pieces that may have had varied production and use modes depending on the sites, regions and periods. A simple morphological categorization (polyhedron, spheroid, bola) is therefore not sufficient to account for this diversity. Perennial and ubiquitous, they were certainly disseminated, adapted and reinvented throughout the Old World during the Paleolithic. In order to corroborate our hypotheses, this functional analysis must be coupled with the study of the production modes of these objects: this is the second part of this study, to be published soon.