Over the past five years, archaeologists have identified more than 1,600 monumental stone structures scattered across a part of Saudi Arabia larger than Italy. The purpose of these ancient stone buildings, dating back more than 7,000 years, has been a mystery to researchers.
Our excavation and research shows these were ritual structures built by ancient shepherds and hunters who would gather to sacrifice animals to an unknown deity – perhaps in response to climate change in ancient times. The study is published today in PLOS ONE.
Discoveries in the desert
In the 1970s, the first archaeological surveys in northwestern Saudi Arabia identified an ancient and mysterious rectangular structure. The structure’s sandstone walls were 95 m long and although it was determined to be a unique site, no further investigation of this unusual site was undertaken.
In the following decades, passengers across the country would see similarly sized “rectangles”. However, one was not excavated until 2018.
These structures are now known as mustatils (Arabic for rectangle). We have studied them over the past five years as part of a larger archaeological survey sponsored by the Saudi Royal Commission for AlUla.
The smallest mustatils are around 20m long, while the largest are over 600m long. Previous work by our team has shown that all Mustatils follow a similar architectural plan. Two thick ends were connected by two to five long walls, creating up to four courtyards.
Access to the Mustatil was through a narrow entrance in the base. There would then have been a long walk, perhaps in the form of a procession, to the ‘head’ where the main ritual activity took place.
Previous studies have found the Mustatils to be at least 7,000 years old, dating to the end of the Neolithic period.
In 2019-2020 we conducted excavations at a Mustatil site named IDIHA-0008222. The structure made of unworked sandstone is 140 m long and 20 m wide.
Excavations in the Mustatil’s head revealed a semi-subterranean chamber. In this chamber were three large stones standing vertically. We have interpreted these as “betyles” or sacred standing stones representing unknown ancient deities.
Surrounding these stones were well-preserved horns of cattle, goats, and gazelles. The horns are so well preserved that we mostly find the horn sheath, which is made of keratin — the same substance as hair and nails. We found only the upper cranial elements of these animals: teeth, skulls, and horns. This suggests a clear and concrete selection of offers.
Further analysis indicates that the majority of these remains belonged to male animals, and the cattle were between 2 and 12 years old. Their slaughter would have represented a significant portion of a community’s wealth, suggesting that they were high-value offerings.
Current evidence indicates that the Mustatils lived between 5300 and 4900 BC. when Arabia was green and humid. However, within a few generations, the ancient inhabitants of Saudi Arabia began to reuse these structures, this time to bury human body parts.
At IDIHA-0008222, a small structure was built next to the Mustatil. Inside were a partial foot, five vertebrae, and several long bones.
Their placement suggests that soft tissue was still present when they were buried. Forensic anthropologists were able to determine that the remains likely belonged to a person between the ages of 30 and 40.
Our work on other Mustatils has revealed similar deposits of human remains. Were these remains buried in an attempt to claim ownership of the structure, or in some form of later ritual? These questions have yet to be answered.
Point to water
The Mustatils are changing our view of the Neolithic not just in Arabia but throughout the Middle East. The sheer size of these structures and the amount of labor involved in their construction suggests that multiple communities came together to create them, most likely as a form of group bonding.
Furthermore, their widespread distribution in Saudi Arabia suggests the existence of a common religious belief maintained across a vast and unprecedented geographical distance. Fewer than ten mustatils have been excavated at this time, so our understanding of these structures is still in its infancy.
The key question to answer is “why were they built?” A surveying trip by our team may have partially solved this mystery.
When we plotted these structures after rain, we found that almost all of the mustatils pointed to areas that contained water. Perhaps the mustatils were constructed and the animals sacrificed to the god or gods to ensure the continuation of rain and the fertility of the land.
There remains the possibility that the Mustatils were built in response to climate change as the region became increasingly arid, as it is today.
Our investigation of the Mustatils is ongoing. Our new project at the University of Sydney focuses on understanding why these monumental structures and others were built and what led to their demise.
We hope that future excavations and analysis will reveal further insights into the life and death of the Mustatils and the people who built them.
Read more: Climate and the rise and fall of civilizations: a lesson from the past