Reading Closed Cuneiform Tablets Using High-Resolution Computed Tomography
2020–2025
RFA09
Photo: Karsten Helmholz
An enveloped cuneiform clay tablet inside the Tungsten chamber of ENCI.
Photo: Karsten Helmholz
Heavy lifting: Overall, the device weighs about 430 kg and the dimensions are 107 x 142 x 55 cm (LxHxW). Here, the brand new device is being delivered to the premises of the Cluster for the first time.
Photo: Karsten Helmholz
3D-printed sample holder with a kinematic mount for convenient and protective handling; it is designed to hold samples measuring up to 10 x 20 x 5 cm in size.
Photo: Karsten Helmholz
The electronic rack is the core of the CT scanner, housing 20 TB of data storage and a substantial computing capacity.
Photo: Karsten Helmholz
The sample holder is mounted on a stage that can be rotated and moved in three directions. Surrounding the set-up is a Tungsten chamber providing shielding for the X-rays.
Photo: Karsten Helmholz
Microfocus X-ray tube specialised for high-resolution scans of thick material, such as cuneiform tablets.
Photo: Karsten Helmholz
ENCI and the team running it in the laboratory of the Cluster. From left to right: Sebastian Bosch (Manager of instrumental analytics at the CSMC laboratory), Samaneh Ehteram (Research associate at CSMC/DESY), Patrik Wiljes (Mechatronics engineer at DESY), Christian Schroer (Principal Investigator of RFA09), Andreas Schropp (Senior scientist at DESY), Philipp Paetzold (Master student at UHH/DESY), Ralph Döhrmann (Senior engineer at DESY).
Photo: Andreas Schropp
February 2024: ENCI arrives at the Louvre in Paris.
Photo: Andreas Schropp
The museum has one of the largest collection of ancient clay tablets in the world.
Photo: Véronique Pataï
The ENCI team during the measurements in the basement of the museum.
Photo: Andreas Schropp
Samaneh Etheram with a virtual reconstruction of one of the clay tablets.
Photo: Andreas Schropp
The ENCI team in the ancient collection of the museum.
Cuneiform clay tablets from the ancient Middle East document the first two-thirds of recorded human history. Invented around 3400 BCE, cuneiform script was used for three and a half millennia, until the second century CE. From the middle of the third millennium BCE onwards, letters and legal texts were often wrapped in an envelope made of an additional layer of clay. These envelopes, repeated parts of the inner tablet and, along with seal impressions of the parties and witnesses, provided certification for legal texts. The letter envelopes protected both the confidentiality of the text and the material integrity of the tablets during their journey through mountains and the desert. Sender and recipient names were written on the envelopes, which were sealed with the sender’s cylinder seal. In order to read the message, the envelope had to be broken, destroying the artistic seal impression in the process.
Such opened letters then were kept in archives, where they can be found today. About a million clay tablets have survived to this day. However, sometimes a letter did not reach its intended recipient, remaining in its clay envelope for thousands of years. The same applies to legal documents that were still valid when the building housing them was destroyed. In order to preserve the miniature scenes of seal impressions intact, envelopes are no longer opened in museums. Other ways need to be used to reveal the inside of the envelope, using X-rays for instance to penetrate the envelope and to read the hidden texts. X-ray microtomography is ideal for this task, giving the full 3D structure of an artefact. However, we were faced with a serious constraint: The millennia-old cuneiform tablets are too fragile to be removed from their place of preservation in museums, and the X-ray tomographic scanners available commercially weigh several tons and cannot be easily moved. The only solution was therefore to develop, build, and bring into application a portable high-resolution X-ray tomographic scanner for encased cuneiform tablets, enabling us to read sealed cuneiform texts without breaking the envelope [25/1/2024 ‘ENCI Gives Us Access to a Wealth of Source Material’, Logbook: The CSMC Blog, https://www.csmc.uni-hamburg.de/about/blog/2024-01-29-enci-michel.html].
Non-invasive, virtual unpacking of enclosed cuneiform
ENCI was conceived to enable high-resolution X-ray CT of cuneiform tablets directly inside museums, where artefacts cannot be transported and where no radiation-controlled infrastructure is available. Reading tablets up to 10 cm in size with a resolution of below the width of a hair requires high X-ray energies (up to 180 keV), which in turn demand substantial shielding to keep dose rates below the level for operation in public spaces. At the same time, the scanner must be light enough to be carried through narrow archives and assembled in a simple environment.
These physical constraints dictated a compact, highly conical imaging geometry with short source–sample–detector distances, locally optimised shielding thicknesses, and a fully modular design. ENCI therefore consists of eight interlocking components, each typically 50 kg in weight, that minimise the shielded surface area while given full radiation protection. Integrated computing and controls allow fast acquisition, on-site reconstruction and completely offline operation, making ENCI a self-contained, transportable micro-CT scanner for cultural-heritage studies. [25/1/2024 ‘The Challenge is to Combine Lightweight Construction and Radiation Protection’, Logbook: The CSMC Blog, https://www.csmc.uni-hamburg.de/about/blog/2024-01-29-christian-schroer.html]
ENCI was first tested in December 2023 on a few encased cuneiform tablets from the Böhl collection in Leiden, which were brought to Hamburg by C. Waerzeggers [25/1/2024: ‘Using the World’s First Mobile Computer Tomography Device to Decipher Hidden Texts’]. After several months of formalities with the museum administration and the nuclear safety authority, the instrument was transported to the Musée du Louvre in February 2024, in order to scan twelve encased cuneiform tablets from Iraq and Anatolia. The computed tomographic scanner ENCI was officially inaugurated in Hamburg on the 30 April 2024 ‘X-Ray views into Ancient Clay Envelopes’, Logbook: The CSMC Blog, https://www.csmc.uni-hamburg.de/about/blog/2024-04-30-enci-inauguration.html].
After getting the authorisation from the Ministry of Culture in Türkiye and fulfilling formalities for the import/export, the transportation of the instrument, and for radiation safety in Türkiye, ENCI was installed at the Museum of Anatolian Civilisations in Ankara during two long missions in September and October 2024 and 2025. The team scanned there over one hundred and fifty sealed envelopes [2/10/2024 ‘ENCI at Work in Ankara’, CSMC News 2024, https://www.csmc.uni-hamburg.de/news/2024-10-01-enci-in-ankara.html and 16/10/2025 ‘ENCI Returns from Türkiye: https://www.csmc.uni-hamburg.de/news/2025-10-16-enci-tuerkiye.html]. During the second mission to Turkiye, ENCI was also set up in the Kayseri Archaeological Museum. Tomograms were recorded of several artefacts made of clay, glass, stone, and metal, which were found during the excavations of the Bronze Age site of Kültepe, located 22 km from the city. In late 2025, ENCI also visited the Hilprecht clay tablet collection in Jena.
During these missions, the Assyriologist, archaeometer, physicists and computer scientist worked together, with each person in charge of specific operations. The encased tablets were placed in the chamber of the tomographic scanner and scanned. The tomograms were then reconstructed and processed further to extract, segment and visualise isosurfaces using software designed specifically for this purpose. This workflow enabled the Assyriologist to read the text on the hidden tablets and to discover various inclusions in the clay, such as stones and organic and animal remains like seeds and snails. It was also possible to occasionally discover differences in the clay composition of a tablet and its corresponding envelope, suggesting that they were prepared in different locations and at different times. Lastly, the shaping of the tablet clay and the techniques used to envelop the tablets could be better understood.
Clay envelope, Louvre Museum No. Ao8295: The envelope (top) and the letter contained in the envolope (bottom).
People
Project lead: Christian G. Schroer, Cécile Michel, Stephan Olbrich
Research Associates: Samaneh Ehteram, Andreas Beckert