Archaeomagnetism in Mesopotamia

Archaeomagnetism in Mesopotamia: Brick inscription of Nebuchadnezzar II. Courtesy Nathan Steinmeyer.

Inscribed bricks are found throughout ancient Mesopotamia, where they were used for millennia to mark the monumental constructions of kings and officials. Now, they may also help archaeologists better date ancient events. Publishing their results in the journal Proceedings of the National Academy of Sciences, an international team of researchers sampled 40 inscribed bricks dating from the third through first millennia BCE to identify the strength of the earth’s magnetic field at the time the bricks were made.

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Dating a Brick

Why does knowing the strength of the earth’s magnetic field help date past events? Through analysis of archaeomagnetism, archaeologists identify the shift of the planet’s magnetic strength over time and compare that to levels recorded in excavated objects. This can establish a relative chronology of objects, but to create an absolute chronology, archaeologists need to test their results against objects that are already securely and precisely dated. This is where inscribed clay bricks come in.

Used extensively throughout Mesopotamia, these bricks were stamped with royal inscriptions–written in Sumerian or Akkadian–that mention the kings associated with specific building projects. Utilizing established king lists, scholars already have accurate dating for when most Mesopotamian kings reigned, with only a few short periods of uncertainty. With this data, the team was able to take the magnetic results provided by the bricks to create a precise baseline of the magnetic field at specific points in time. In general, this method provides a far more accurate method of dating than other “absolute” dating methods such as radiocarbon dating, which often has an uncertainty of a century or more. As minor variations in the magnetic field occur regularly, archaeomagnetism allows objects to be dated to within just a few decades.

“Historical inscriptions have always been instrumental in archaeological research to synchronize important events,” study co-author Shai Gorin told Bible History Daily. “The new form of archaeomagnetic analysis we applied to inscribed Mesopotamian clay artifacts has shown that independent relative dating can now be combined with the data in the historical inscriptions themselves to create better dating sequences.”

Regional map of the Levant and Mesopotamia, illustrating the locations of high-quality archaeointensity samples from previous studies and this study. Courtesy Howland et al.

While the shift in the earth’s magnetic field has been studied extensively in many regions, including the Levant, subtle differences can make those data inaccurate for other regions, requiring independent verification of the baseline for each region of study. This is one of the first large-scale studies ever conducted for Mesopotamia. It is also one of the first times that inscribed bricks have been sampled, as opposed to pottery fragments or standard mudbricks, which cannot be dated as precisely. When asked about this by Bible History Daily, study co-author Erez Ben-Yosef replied, “Ancient inscribed objects are usually part of museum exhibitions and important collections. And although damage is minimal, sampling for magnetic analyses is destructive, and accordingly getting permission to study these objects is not easy.”

Although, Ben-Yosef said, the team’s “research contributes significantly to the development of an archaeomagnetic dating reference for Mesopotamia, one of the key regions in the history of human civilizations,” the number of samples is still much lower than other regions, and the team hopes that this and other projects will continue to add to the baseline data.

Already with their data, however, the team was able to answer some outstanding questions. One is whether the so-called “Levantine Iron Age Geomagnetic Anomaly” existed in Mesopotamia. This was a period between 1050 to 550 BCE when the earth’s magnetic field was unusually strong. Although this anomaly has been identified in numerous regions beyond the Levant, previous research had not identified it in Mesopotamia. This new study, however, demonstrated that it existed there as well.

The team further suggests that their evidence might answer one of the biggest debates in Mesopotamian history: the length of the Babylonian “dark ages,” which spanned from the end of the Old Babylonian period (c. 2004–1595 BCE, standard chronology) to the Kassite period (c. 1475–1155, standard chronology). “Based on a comparison between our results and the well-established curve for the Levant, we carefully suggest that the magnetic data support the Low Chronology for Mesopotamia,” said Ben-Yosef. If further confirmed, this conclusion would shift much of the history of Mesopotamia before the mid-second millennium by around 50 years.