Archaeology through the eyes of physics

Physicists and archaeologists worked side by side to analyse ancient clay, wood and metal artefacts from the Archaeological Museum of Lilybaeum (Marsala) through non-destructive and non-invasive forefront techniques.

X-ray computed tomography (CT) was indeed performed on archaeological finds by means of a dedicated transportable apparatus. The instrumentation was designed to suit a wide range of objects and composed by a powerful micro-focus X-ray tube (with maximum voltage of 130 kV and maximum current of 0.5 mA), a large-surface solid-state detector and a rotational stage.

The analysis was carried out in the framework of the Lilybaeum Project, involving the Regional Archaeological Museum of Lilybaeum, the University of Geneva and the "Enrico Fermi" Historical Museum of Physics and Study&Research Centre, in collaboration with the University of Bologna and the INFN Unit of Bologna.

A special collection of intact small clay jars and rattles found in the graves of the Punic necropolis of Lilybaeum (3^rd-2^nd centuries BC) was analysed in situ for the first time with the above equipment. The inspection of the X-ray CT slices in combination with 3D renderings revealed details that helped archaeologists assessing the state of preservation of the artefacts and reconstructing the ancient manufacturing processes. For instance, the shape and dimensions of a clay pellet inside the rattles could be documented, inclusions and cracks in the fabric were clearly visible as well as voids located where additional clay material was attached to the body of the jar (as in the case of added bases or decorative elements). In some cases, the homogeneity of the thickness of the walls, the presence of regular rings together with the direction of the tiny air vacuoli observed in the fabric through magnification of the tomographic slices was consistent with the use of the turning wheel technique.

Tomographic slices of one of the wooden fragments of the Punic Ship showing the mortise-and-tenon joints and many other details. (Credit: The European Physical Journal Plus, SIF – Springer)

Moreover, the first ever X-ray CT was performed on two wooden elements of the hull of the only existing wreck of a Punic ship sunk in front of Marsala during the Punic Wars, which is preserved at the Archaeological Museum. The shipwreck, dated to the 3^rd Century BC, was discovered and recovered during the 1970's by Honor Frost, a pioneer in underwater archaeology. The Punic ship was restored in collaboration with the Sicilian authorities and the British School at Rome for display in the local Archaelogical Museum.

The precise tomographic images recently obtained using X-ray CT of fragments of the wreck have shown the details of the mortise-tenon joints, including the dowels and metal nails used by the ancient carpenters to assemble the elements of the planking. Moreover, thanks to the high resolution of the tomography, the morphology and growth rings of the wood could be observed and measured. These observations are of great relevance for identifying timbers and understanding shipbuilding as well as for dendrochronology.

The Lilybaeum Project provided interesting new data on artefacts made of different materials (clay, wood, metal) as well as on ancient crafts. Furthermore, it opened unexpected research questions and demonstrated, once more, the strong potential of interdisciplinary approaches, together with the importance of non-destructive, non-invasive and transportable investigating techniques as key tools in archaeological research.

This study was published in EPJ Plus whose aims and scope include physics techniques applied to cultural heritage. The journal has already published a number of interesting topical issues on this matter in the last few years.