Teetering on a small island in the middle of Siberia lies the mysterious ruins of an ancient fortress. Archeologists have recently ventured to this remote structure and carried out cutting-edge dating technology, concluding the colossal complex was built in 777 CE.
Strangest of all, the complex appears to have never been used, leading to questions about its purpose. Thanks to a new study, however, things are starting to become a little clearer.
Known as Por-Bajin, which translates as “clay house,” the complex consists of 12-meter-high (39 foot) clay walls that run around a 215-by-162 meter (705-by-531 foot) site. It was built on a small island in a lake in the mountains of southern Tuva near the border between Russia and Mongolia by a group of nomadic Uyghurs, a Turkic ethnic group native to the Xinjiang Uyghur Autonomous Region in Northwest China.
Reported in the journal Proceedings of the National Academy of Sciences, researchers from the University of Groningen in the Netherlands and the Russian Academy of Science carried out radiocarbon-based dating on wood from the site to discover when it was built.
The team used a method that closely looks at differing levels of carbon-14, a radioactive isotope of carbon that’s created in the upper atmosphere. Changes in atmospheric carbon-14 were believed to show little variation from one year to the next, but in 2013 scientists discovered that tree rings contained a massive spike in carbon-14 content in the year 775 CE. Armed with this knowledge, it’s possible to date wood from around this area.
“When you find wood at an archaeological site from that period, you can look for the spike by measuring the carbon-14 content of subsequent tree rings,” Margot Kuitems, study author and a postdoctoral researcher at the Centre for Isotope Research at the University of Groningen, explained in a statement.
The carbon-14 spike was discovered in the third ring from the bark, suggesting the site was constructed just a couple of years after 775 CE.
“We knew the tree was felled in 777. Tree ring specialist and co-author Petra Doeve determined that the final, partial ring was created in the spring,” Kuitems added.
This dating also neatly lines up with other historical knowledge and archaeological artifacts from the area. Considering the complex was built in the 8th century CE, the team argues it likely served as a religious monastery. In 777 CE, the leader Tengri Bögü Khan converted the nomadic Uyghur Khaganate empire to a now-extinct religion known as Manichaeism. It's possible the complex was built to serve as a Manichaean monastery. However, Bögü Khan was promptly killed in an anti-Manichaean rebellion in 779 CE, which would explain why the complex was never used.