Ancient Plant DNA Extracted from 2,900-Year-Old Assyrian Brick
DNA testing in an archaeological context has been improving by leaps and bounds, resulting in many new discoveries relating to ancient human, animal and plant genetics. New ground in DNA analysis of the past is being broken all the time. In a prime illustration, a team of scientists from Denmark and the United Kingdom extracted intact ancient plant DNA from a clay brick used during the construction of a grand palace in the Assyrian capital of Nimrud in the ninth century BC. This is the first time such a feat has ever been accomplished.
“With this research we have made the pioneering discovery that ancient DNA, effectively protected from contamination inside a mass of clay, can successfully be extracted from a 2,900-year-old clay brick,” the study authors wrote in a paper published in Scientific Reports. “We encourage future research into this subject, as the scientific prospects for this approach are substantial, potentially leading to a deeper understanding of ancient and lost civilizations.”
Ruined remains of the Palace of Ashurnasirpal II at Nimrod on the Tigris River in modern-day Iraq. Ancient plant DNA has been discovered trapped inside a brick discovered during excavations. (Public domain)
Ancient Plant DNA Trapped in a Brick Found in the Remains of a Palace
The clay mudbrick analyzed in this study was once part of the opulent palace of the Neo-Assyrian king Ashurnasirpal II, who ruled the lands of modern-day Iraq from 883 to 859 BC. Researchers know this because of its cuneiform inscription, which identifies the brick directly as “property of the palace of Ashurnasirpal, king of Assyria.”
This particular brick was recovered by British and Danish archaeologists during excavations in the ruins of the ancient Assyrian capital city of Nimrud—known as Kulhu to the Assyrians—in 1949. It was eventually sent to the National Museum of Denmark for safekeeping and to be put on display for the public.
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When the brick arrived in Denmark it had already broken into two pieces horizontally. Mudbricks of this type are strong but subject to cracking and when the pieces of the brick were examined in 2020 the bottom half suddenly broke in two vertically.
Previously, such a development would have been viewed as a regrettable accident. But in this instance the cracking and splitting of the ancient brick provided a golden opportunity to expand the boundaries of ancient DNA testing in a fascinating new direction.
Intrigued by the possibilities, a new team of British and Danish researchers with expertise in chemistry, biology and genetics, asked for access to the freshly broken brick, to see if it would be possible to remove DNA samples from the newly exposed interior. While such a thing had never been done before, the science of DNA has advanced to the point where it seemed theoretically possible.
The five sampling points on the surface of the brick from which ancient plant DNA has been extracted. (Troels Pank Arbøll / CC BY 4.0)
A Miniature Ancient Assyrian Ecosystem Preserved in Clay
In ancient Mesopotamia, craftspeople made this type of brick by drying a mixture of clay-laden mud, straw and animal dung in the sun. No extreme heat was used to manufacture mudbricks, which meant that any genetic materials absorbed by the mud from the surrounding environment could be trapped inside the brick and preserved indefinitely.
As it turned out, the scientists had no trouble finding well-preserved genetic samples on the newly exposed brick surface. After sequencing the ancient plant DNA they’d removed, the scientists compared their results to modern genetic samples taken from the region. They also studied historical records to find out which specific species of plant were known to have existed in the area around Nimrud in Neo-Assyrian times. Through this type of comparative analysis, the scientists were able to identify 34 distinct types of plants, including ancient versions of cabbages, laurels, heathers and local grasses.
“Because of the inscription on the brick, we can allocate the clay to a relatively specific period of time in a particular region, which means the brick serves as a biodiversity time-capsule of information regarding a single site and its surroundings,” explained Assyriologist and study co-author Dr. Troels Arbøll in a University of Oxford press release. “In this case, it provides researchers with a unique access to the ancient Assyrians.”
Nimrud, or Kulhu, was the capital of the Neo-Assyrian Empire when Ashurnasirpal II was king. Because so many people lived there, many of the plants that grew in the region would have been harvested or cultivated as sources of food, medicine, ornamentation or fiber for making clothes, ropes or other useful items. Consequently, the newly recovered ancient plant DNA samples could give researchers some idea of which plants the ancient Assyrians actually relied on to meet their cultural and societal needs.
Dr. Sophie Lund Rasmussen at the excavation site where the brick containing the ancient plant DNA was found. (Sophie Lund Rasmussen)
Genetic Testing is Revolutionizing Archaeology
The success of this latest DNA testing project shows the incredible range of possibilities that are opening up for experts who study archaeology and ancient history as genetic analysis grows in sophistication.
Fortunately, many ancient societies created cultural objects and used building materials made from clay, artifacts which are frequently collected during archaeological digs. Now that scientists know they might have absorbed and preserved DNA samples from plants, animals, insects or even humans, any such items with exposed interiors could be used as source materials for genetic research.
This could open up new avenues of exploration for scientists from many different fields who share an interest in lost civilizations and ecosystems, and who could benefit in one way or another from the analysis of ancient genetic samples.
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“This research project is a perfect example of the importance of interdisciplinary collaboration in science, as the diverse expertise included in this study provided a holistic approach to the investigation of this material and the results it yielded,” said University of Oxford ecologist and study co-author Dr. Sophie Lund Rasmussen.
New ground in the field of ancient DNA analysis has definitively been broken as a result of this innovative research. Where it may all lead is still to be determined.
Top image: The clay brick from the National Museum of Denmark and from which scientists have extracted ancient plant DNA. Source: Arnold Mikkelsen og Jens Lauridsen
By Nathan Falde