TAU researchers use earth’s magnetic field to verify Old Testament event

One of the studied burnt mudbricks. Photo credit: Dr. Yoav Vaknin.

New technology interprets archaeological findings from biblical era

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Research from Tel Aviv University (TAU) and three other Israeli universities will enable archaeologists to identify burnt materials discovered in excavations and estimate their firing temperatures. The new technique can determine whether a certain item, such as a mud brick, underwent a firing event even at relatively low temperatures, from 200°C (about 400°F) and higher. This information can be crucial for correctly interpreting the findings.

Applying their method to findings from ancient Gath (Tell es-Safi in central Israel), the researchers validated the Biblical account from 2 Kings 12,18: “About this time Hazael King of Aram went up and attacked Gath and captured it. Then he turned to attack Jerusalem.” (2 Kings 12, 18).

The multidisciplinary study was led by Dr. Yoav Vaknin from the Sonia and Marco Nadler Institute of Archaeology, Entin Faculty of Humanities, at TAU and the Palaeomagnetic Laboratory at The Hebrew University. Other contributors included Professor Ron Shaar from the Institute of Earth Sciences at The Hebrew University, Professors Erez Ben-Yosef and Oded Lipschits from the Nadler Institute at TAU, Professor Aren Maeir from the Martin (Szusz) Department of Land of Israel Studies and Archaeology at Bar-Ilan University, and Dr. Adi Eliyahu Behar from the Department of Land of Israel Studies and Archaeology and the Department of Chemical Sciences at Ariel University. The paper has been published on October 9, 2023, in the scientific journal PLOS ONE.

“Throughout the Bronze and Iron Ages, the main building material in most parts of the Land of Israel was mud bricks,” Professor Lipschits explains. “This cheap and readily available material was used to build walls in most buildings, sometimes on top of stone foundations. That’s why it’s so important to understand the technology used in making these bricks.”

The new method relies on measuring the magnetic field recorded and “locked” in the brick as it burned and cooled down. In the second stage of the procedure, the researchers gradually “erase” the brick’s magnetic field using a process called thermal demagnetization. This involves heating the brick in a special oven that neutralizes the earth’s magnetic field. The heat releases the magnetic signals, which once again arrange themselves randomly, canceling each other out, and the total magnetic signal becomes weak and loses its orientation.

The researchers fired mud bricks under controlled conditions of temperature and magnetic field, measured each brick’s acquired magnetic field, then gradually erased it. They found that the bricks were completely demagnetized at the temperature at which they had been burned, proving that the method works.

“Our approach enables identifying burning which occurred at much lower temperatures than any other method,” Dr. Vaknin says. “Most techniques used for identifying burnt bricks are based on actual changes in the minerals, which usually occur at temperatures higher than 500°C [932°F], when some minerals are converted into others.”

After proving the method’s validity, the researchers applied it to a specific archaeological dispute: Whether a specific brick structure discovered at Tell es-Safi — identified as the Philistine city of Gath, home of Goliath — was built of pre-fired bricks or burned on location. The prevalent hypothesis, based on the Old Testament, historical sources, and carbon-14 dating attributes the destruction of the structure to the devastation of Gath by Hazael, King of Aram Damascus, around 830 BCE. But a previous paper by researchers including Professor Maeir, head of the Tell es-Safi excavations, proposed that the building had not burned down, but rather collapsed over decades, and that the fired bricks found in the structure had been fired in a kiln prior to construction. If this hypothesis were correct, this would be the earliest instance of brick-firing technology discovered in the Land of Israel.

To settle the dispute, the current research team applied the new method to samples from the wall at Tell es-Safi and the collapsed debris found beside it. The findings were conclusive: The magnetic fields of all bricks and collapsed debris displayed the same orientation, north and downwards. “Our findings signify that the bricks burned and cooled down in-situ, right where they were found, namely in a conflagration in the structure itself, which collapsed within a few hours,” Dr. Vaknin says. “Had the bricks been fired in a kiln and then laid in the wall, their magnetic orientations would have been random. Moreover, had the structure collapsed over time, not in a single fire event, the collapsed debris would have displayed random magnetic orientations.

“We believe that the main reason for our colleagues’ mistaken interpretation was their inability to identify burning at temperatures below 500°C. Since heat rises, materials at the bottom of the building burned at relatively low temperatures, below 400°C, and consequently the former study did not identify them as burnt. At the same time, bricks in upper parts of the wall, where temperatures were much higher, underwent mineralogical changes and were therefore identified as burnt, leading the researchers to conclude that they had been fired in a kiln prior to construction. Our method allowed us to determine that all bricks in both the wall and debris had burned during the conflagration: those at the bottom burned at relatively low temperatures, and those that were found in higher layers or had fallen from the top – at temperatures higher than 600°C.”

“Our findings are very important for deciphering the intensity of the fire and scope of destruction at Gath, the largest and most powerful city in the Land of Israel at the time, as well as understanding the building methods prevailing in that era,” Professor Maeir concludes. “It’s important to review conclusions from previous studies, and sometimes even refute former interpretations, even if they came from your own school.”

"It's important to review conclusions from previous studies, and sometimes even refute former interpretations, even if they came from your own school."