Vast stone structures littering the Saudi Arabian desert are as old as 7,000 years, making them some of the world’s most ancient monuments, according to new research by an international team of archaeologists.
Researchers said the structures were likely used for ritual purposes by ancient pastoralists, as they made the transition to agriculture during a conducive climactic window on the Arabian peninsula.
The mysterious structures are rectangular, with parallel stone platforms at both ends, like elevated end zones in a football field, and long, thin walls connecting the platforms. The largest of the structures is 616 meters (2,021 feet) in length.
They are located in a variety of landscapes and settings in the desert environment and have been dubbed “mustatils” by archaeologists — the Arabic word for rectangle.
At least one was confirmed as the oldest large stone structure on the Arabian peninsula.
“The vast scale of these structures makes them among the most spectacular examples of prehistoric monumental architecture anywhere in the world,” the researchers wrote.
A team headed by Dr. Huw Groucutt from Germany’s Max Planck Institute, alongside the Saudi Ministry for Tourism and other Saudi and international collaborators, carried out the first ever detailed research on the mustatils.
There have been relatively few studies of prehistory in Saudi Arabia, especially outside of its southeast region. Human habitation on the peninsula dates back to at least the Middle Pleistocene era, which spanned from 777,000 years ago until 126,000 years ago.
As archaeology has picked up pace in the kingdom over the past decade, researchers have identified millions of stone structures made of piled rocks, including burial tombs and hunting traps.
Cairns, small funeral structures, are widespread and date from the Neolithic era until around 600 CE. “Desert Kites,” described by the researchers as “mass-kill hunting traps,” are also common in northern Arabia, but have not been thoroughly studied. In nearby Jordan, one desert kite was dated to around 8,000 BCE.
Some of the structures were used by early hominins hundreds of thousands of years ago.
The mustatils, which were previously located with satellite imagery, were the most intriguing of these ancient constructions.
The researchers used satellite imagery to newly identify 104 mustatils around the southern border of the Nefud Desert, in the northern part of the peninsula, some 250 miles from the Israeli city of Eilat. They followed up by conducting field work at a select group of the structures.
The sites were evenly distributed around the desert region, but often clustered together in groups. Mainly, they were built on raised areas of the landscapes, and many were located near ancient lakes and wetlands, but the locations and topography of the sites varied widely.
There were no clear patterns to the structures’ directional orientation, but mustatils in clusters tended to be oriented in the same direction.
The average length of the structures is 160 meters (525 feet), with an average width of 22 meters (72 feet). A single platform could contain hundreds of tons of rocks.
The connecting walls between the platform are less than half a meter tall, with no openings. At some sites, these walls were made out of rocks cleared from between the platforms, suggesting that the space between the platforms was the point, and not the low walls themselves.
Hundreds of the structures had been found previously, especially around Khaybar, an oasis and historical site farther south made infamous by a 7th-century battle when a Muslim army massacred Jews there.
In the new study, the team said they found few artifacts besides stones at the sites, such as tools or ceramics, suggesting that the artifices were not for habitation or utilitarian purposes, such as animal pens. The lack of artifacts and clear purpose for the structures suggests they were used for ritual or social purposes.
At one site, the team found charcoal in one of the platforms, which they dated to around 5,000 BCE using radiocarbon dating, meaning the structure is 2,000 years older than the pyramids in Egypt.
The researchers said that the mustatils are not the oldest known structures, but are on a “uniquely large scale for this early period.”
The team found the bones of wild animals among the ruins, including some that were either domestic cattle or wild auroch. The bones of wild animals at the sites suggest a blended culture of agriculture and hunting as the people transitioned to a pastoral lifestyle, and could hint to animal sacrifices.
At another site, the team found a slab painted with a geometric pattern. The rock was placed on a platform and would have been clearly visible to people standing within the enclosed space, further suggesting a ritual use for the sites. The pattern on the rock has not been been identified anywhere else.
“Our interpretation of mustatils is that they are ritual sites, where groups of people met to perform some kind of currently unknown social activities,” said lead researcher Groucutt. “Perhaps they were sites of animal sacrifices, or feasts.”
At the time of their construction, the region was going through the most recent “Green Arabia” period, a window of time with increased rainfall, making the area more vibrant, creating grasslands and some lakes, wetlands and rivers.
The mustatils around Khaybar are often located near wadis which would have held water after heavy rainfall.
The structures likely represent a significant cultural shift in the region amid the changing landscape.
Pastoralism began in the area as early as 6,800 BCE, and was better established by 6,000 BCE, but the area would have still been harsh to live in due to periodic droughts.
The team theorized that the mustatils were built for social purposes and communal cooperation in the challenging environment, both in the process of building them, and in rituals carried out within them. At some of the sites, several structures were constructed alongside each other, suggesting that act of construction itself could have been an exercise in social bonding, the researchers said.
Constructing monuments suggests growing territoriality among the ancient peoples as they transitioned from nomadism into a pastoral lifestyle, and competed for resources such as grazing lands, the researchers said. The transition to agriculture, and defense of resources, would have led to people forming larger group identities.
Similar stone platforms have been located in Yemen, including many with animal bones, suggesting they were used for sacrifices or feasts. At one site in Yemen, dating to 4,400 BCE, researchers found a ring of 42 skulls from domesticated cattle neatly arranged in a circle.
The mustatils are similar to older, smaller structures in the southern Levant, which includes modern-day Israel, including rectangular structures used as cairns and other “cultic” sites, suggesting that people and ideas migrated from the southern levant to Arabia and inspired the mustatils.
The research was published last month in the peer-reviewed scientific journal, The Holocene.