New Technology Interprets Archaeological Findings from Biblical Times

Researchers rely on the Earth’s magnetic field to verify an event mentioned in the Old Testament

— The new study scientifically corroborates an event described in the Second Book of Kings – the conquest of the Philistine city of Gath by Hazael King of Aram.

— The method is based on measuring the magnetic field recorded in burnt bricks. The

researchers: “Our findings are important for determining the intensity of the fire and the scope of destruction in Gath – the largest and most powerful city in the land at the time, and also for understanding construction practices in the region.”

A breakthrough achieved by researchers from four Israeli universities – Tel Aviv University, The Hebrew University of Jerusalem, Bar-Ilan University, and Ariel University – will enable archaeologists to identify burnt materials discovered in excavations and estimate their firing temperatures. Applying their method to findings from ancient Gath (Tell es-Safi in central Israel), the researchers validated the Biblical account: “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). They explain that, unlike previous methods, 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 and up. This information can be crucial for correctly interpreting the findings.

The multidisciplinary study was led by Dr. Yoav Vaknin from the Sonia & Marco Nadler Institute of Archaeology, Entin Faculty of Humanities, at Tel Aviv University, and the Palaeomagnetic Laboratory at The Hebrew University. Other contributors included: Prof. Ron Shaar from the Institute of Earth Sciences at The Hebrew University, Prof. Erez Ben-Yosef and Prof. Oded Lipschits from the Sonia & Marco Nadler Institute of Archaeology at Tel Aviv University, Prof. 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 in the scientific journal PLOS ONE.

Prof. Lipschits: “Throughout the Bronze and Iron Ages the main building material in most parts of the Land of Israel was mud bricks. 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.”

Dr. Vaknin adds: “During the same era dwellers of other lands, such as Mesopotamia where stone was hard to come by, would fire mud bricks in kilns to increase their strength and durability. This technique is mentioned in the story of the Tower of Babel in the Book of Genesis: “They said one to another, Come, let us make bricks and fire them thoroughly. So, they used brick for stone”(Genesis 11, 3). Most researchers, however, believe that this technology did not reach the Land of Israel until much later, with the Roman conquest. Until that time the inhabitants used sun-dried mud bricks. Thus, when bricks are found in an archaeological excavation, several questions must be asked: First, have the bricks been fired, and if so, were they fired in a kiln prior to construction or in situ, in a destructive conflagration event? Our method can provide conclusive answers.”

The new method relies on measuring the magnetic field recorded and ‘locked’ in the brick as it burned and cooled down. Dr. Vaknin: “The clay from which the bricks were made contains millions of ferromagnetic particles – minerals with magnetic properties that behave like so many tiny ‘compasses’ or magnets. In a sun-dried mud brick, the orientation of these magnets is almost random, so that they cancel out one another. Therefore, the overall magnetic signal of the brick is weak and not uniform. Heating to 200°C or more, as happens in a fire, releases the magnetic signals of these magnetic particles and, statistically, they tend to align with the earth’s magnetic field at that specific time and place. When the brick cools down, these magnetic signals remain locked in their new position and the brick attains a strong and uniformly oriented magnetic field, which can be measured with a magnetometer. This is a clear indication that the brick has been fired.

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 in a palaeomagnetic laboratory 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.

Dr. Vaknin: “We conduct the process gradually. At first, we heat the sample to a temperature of 100°C, which releases the signals of only a small percentage of the magnetic minerals. We then cool it down and measure the remaining magnetic signal. We then repeat the procedure at temperatures of 150°C, 200°C, and so on, proceeding in small steps, up to 700°C. In this way, the brick’s magnetic field is gradually erased. The temperature at which the signal of each mineral is ‘unlocked’ is approximately the same as the temperature at which it was initially ‘locked’, and ultimately, the temperature at which the magnetic field is fully erased was reached during the original fire.”

The researchers tested the technique in the laboratory: they fired mud bricks under controlled conditions of temperature and magnetic field, measured each brick’s acquired magnetic field, and 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.