Clay bricks from the construction projects of ancient kings record a historical “map” of changes in the Earth’s magnetic field, a new study has found.
About 3,000 years ago, for reasons that are not well understood, the strength of the Earth’s magnetic field suddenly rose above modern-day Iraq.
And when that happened, that change was recorded, researchers revealed Monday; this is history literally baked into the bricks of the cities of Iron Age Babylon.
The findings, published in the Proceedings of the National Academy of Sciences (PNAS), provide a rare ancient record of temporal changes in the Earth’s magnetic field and a new guide to the development of ancient Mesopotamia, a pivotal period in Western history.
States such as Uruk, Babylon and Assyria, the first empires of the West, rose in the regions anchored by fertile lands between the flood-prone Tigris and Euphrates rivers.
These administrations helped invent the state mechanism, from urban centers built of adobe and surrounded by high walls; it is “the channeling of resources and human effort on a scale that other forms of political and social organization struggle to keep up with,” as historian Patrick Wyman writes.
For example, according to Wyman, the signature artifact of the earliest regional cities was a type of mass-produced ceramic bowl found throughout the city of Uruk, expressing “a highly unequal and centralized way of organizing the world between superiors and subordinates.” existing in complex status hierarchies.”
But for all their importance, the ruins of these cities present archaeologists with a serious problem: the problem of timing. The most reliable way to determine the age of an organic artifact, from fabric to wood to bone, is to watch the clockwork of the radioactive carbon atoms contained within it.
Effectively counting from the point of death, this type of carbon dating provides a very accurate tool for determining how long ago a person buried in a grave died or when the tree used to make spear or hoe handles was cut down.
But co-author Mark Altaweel, a professor at University College London, said it was useless in dating characteristic objects of the region.
“Some of the most common cultural remains, such as bricks and ceramics, often cannot be easily dated because they do not contain organic material.”
Even when it works, radiocarbon dating can only pinpoint an object’s location within a few hundred years; It is useful in dating very ancient artefacts, but becomes less useful the deeper one goes into recorded history.
But the results announced Monday offer an alternative method for dating ancient bricks and ceramics: a way to link the reigns of ancient kings to fluctuations in the Earth’s magnetic field, the timing of which can be more accurately measured.
Such works are rare. While most bricks in these cities were sun-dried without firing, fired bricks were reserved for particularly prestigious buildings where erosion was a particular concern or for important public structures such as moats, sewers, or pavements.
The fact that they were fired also gives them special scientific significance when it comes to dating: The clay that formed these bricks contained iron oxide, which records the strength of the Earth’s magnetic field when the raw bricks were placed in the kiln. .
To create a new chronology of the history of the region, scientists took small pieces of 32 kiln-fired bricks, each decorated with an inscription heralding the king at that time, from ancient cities in the region, such as Ashur, the capital of Assyria.
By comparing the known chronology of kings on the bricks with the magnetic forces contained within them, scholars have identified unmarked bricks from other regions that bear their own magnetic imprints as evidence of the reign of particular rulers.
In doing so, scientists confirmed two pieces of information long suspected: that the strength of the magnetic field over Mesopotamia increased between 1050 and 550 BC, and that these increases were sometimes quite erratic.
For example, King Henry II, famous in Biblical history for destroying Jerusalem and exiling its elite to the Babylonian Captivity. Different magnetic readings taken from five bricks fired during Nebuchadnezzar’s reign found: [the] intensity of the Earth’s magnetic field” is possible.
But the findings also have much more practical implications for archaeologists. By correlating specific magnetic readings with specific kings, Altaweel said, they can now place ceramic artifacts within years or decades of their creation, creating “an important dating basis that allows others to benefit from absolute dating using archeomagnetism.”
Lead author Matthew Howland of Wichita State University added that this would allow scientists to “estimate the dates of artifacts heated in ancient times.”
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