The Louvre looks inside sealed clay envelopes

18 February 2024

A tomographic scanner, specially designed to provide a high-definition view of cuneiform tablets enclosed in their clay envelopes, has completed its first mission at the Louvre Museum. The adventure of this novel instrument began during a retreat at the German centre of excellence, Understanding Written Artefact, in Hamburg.

Over dinner, in deep conversation with Christian Schroer, head of the PETRA III synchrotron and professor of nanosciences and X-ray optics at Hamburg University, I explained my frustration, as an assyriologist, at not being able to read the text of cuneiform tablets that were thousands of years old and still encased in their clay shells. This is the case for certain contracts whose envelopes bear the seals of the parties and witnesses, as well as a substantial summary of the contract. But the frustration is even greater for letters where only the names of the sender and recipient are legible on the envelope, which also bears the sender's seal.

As a rule, a tomographic scanner of this kind weighs several tonnes, so it cannot be moved, and cuneiform tablets are precious and fragile objects that do not leave the museums where they are kept. But this did not seem insurmountable to Christian Schroer who, with his colleagues, had already designed a very compact technological demonstrator for the European Space Agency (ESA). The challenge was to design an instrument that could be transported.

A team of physicists, engineers and technicians from DESY (Deutsches Elektronen-Synchrotron) set to work under the direction of Christian Schroer and designed a transportable, very high-definition tomographic scanner that was named ENCI (Extracting Non-destructively Cuneiform Inscriptions), in homage to Enki, the Sumerian god of fresh underground waters and wisdom. The researchers had to reconcile an intensity of radiation that could penetrate a clay tablet, with the lightest possible protection against radiation. In the end, ENCI weighed 420 kg, of which 200 kg constituted the tungsten radiation shield. To achieve this, the radiation chamber was calibrated as accurately as possible on a replica of a tablet in an envelope that I had made using the largest known example as a model.

At the beginning of February 2024, ENCI made its first trip to the Louvre Museum. Dismantled like a 3D jigsaw puzzle and packed into eight custom-made crates, it travelled by road and was reassembled in the basement of the Louvre. The entire project team was present, and we were able to analyse twelve contracts and administrative texts from the end of the 3rd millennium and the beginning of the 2nd millennium that had been selected in agreement with the curators of the Department of Oriental Antiquities.

ENCI produces images of the objects in slices of around ten microns, making it possible to assemble the image of the envelope and the tablet enclosed inside it by following the sometimes very narrow empty space between the surface of the tablet and the inside of the envelope. The tablet is thus virtually visible and can even be 3D printed. Assyriologists can then decipher text that has been hidden for millennia. The images produced by ENCI also allow us to observe the quality of preparation of the clay, which often contains many irregularities, small stones and organic remains, and the shaping of the tablet and the envelope in several layers of clay. Different practices can be distinguished, depending on the period and the place where these objects were made, between southern Iraq and central Anatolia.

The images produced by the tomographic scanner reveal a wealth of information, and we can't wait to take ENCI to the Museum of Anatolian Civilisations in Ankara, where several hundred letters encased in clay for more than 4,000 years are waiting to be deciphered.

The Franco-German project team (CNRS - DESY / CSMC-UWA) in the Khorsabad courtyard of the Louvre Museum: from left to right, Cécile Michel (co-PI, assyriologist), Andreas Schropp (physicist), Andreas Beckert (computer scientist), Christian Schroer (co-PI, physicist), Philipp Pätzold (physics student), Samaneh Ehteram (technician), Matthias Bohn (engineer). Missing from the photo are Ralph Döhrmann (engineer) and Patrik Wiljes (engineer).