Amid burnt-orange cliffs and monolithic outcrops of weather-sculpted sandstone about an hour’s drive from AlUla in northwest Saudi Arabia, archeologists Melissa Kennedy and Hugh Thomas are walking across a prehistoric lakebed in search of a rectangle of stones. Only a wafting breeze keeps the desert heat from being unbearable.
What they seek is a mustatil
(rectangle, pronounced moos-ta-TEEL) that they helped excavate in 2019, before the COVID-19 pandemic shut down travel. Kennedy and Thomas have come from the University of Western Australia to join local and other international colleagues to probe a mystery: why there are more than 1,000 rectangles of stones laid out in seemingly random locations across a region twice the size of Portugal.
The desert hasn’t always been here. Some 7,000 years ago, grasslands, dotted with lakes and coursed with rivers, covered the western Arabian Peninsula. Evidence abounds of the richness of human habitation over the long era that followed the last ice age until the region, along with northern Africa, began drying out some 5,000 years ago.
The region fairly teems with other types of stone structures—mostly cairns, animal traps and tombs—and thousands of drawings on stones and cliffs depict giraffes, cattle, humans and more. Most of these are largely self-evident as to their functions. But not the mustatils. No one knows why they were built, let alone in such numbers and with such variety in size and proportion.
Mustatils are among the oldest of the world’s known, large-scale stone structures. Built of local, undressed rocks, they typically consist of two platforms, each about 2 to 3 meters wide, set on each end of the rectangle. They are connected by thin, parallel walls that vary in length from tens to hundreds of meters. Because these walls appear to have stood only about half to a full meter high, they are clearly too low to have made mustatils useful as animal enclosures. Some mustatils are isolated; others were built in pairs; still others in groups; and they appear in landscapes from hillslopes to relatively flat ground. They have no apparent preferred orientation. A few artifacts such as animal remains and stone tools have been discovered in them, and very little around them. Many appear only faintly above the surface—an indication that there may yet be more beneath the sands.
While the mustatils have been known to local Bedouin and others for centuries or even millennia, it was not until 2018 that the first formal archeological excavation was undertaken. Supplemented by satellite imagery, aerial surveys sponsored by the Saudi Royal Commission for AlUla (RCU) have now mapped more than 1,000 mustatils, yet so far fewer than a dozen have been excavated.
While archeologists are in near-unanimous agreement that mustatils likely served ritual functions, that does not begin to answer the many other questions: How old are they? Why were they made in that form? Why are there so many? Why is there so far no evidence of occupation near any of them? And if they indeed had a ritual function, what did that look like? How did that ritual require or favor this construction? What did it aid? To begin to address these questions, says Kennedy, “at the start our main aim was to work out when these structures dated to and what were their purposes.”
As archeologists that meant one thing: Dig—carefully.
“We decided to excavate our first mustatil based on a combination of the aerial photographs and our later ground survey,” explains Kennedy, who is also the field director for the Aerial Archaeology in the Kingdom of Saudi Arabia (AAKSA). The mustatil they selected measures 140 meters long by 22 meters wide. It “looked promising from the aerial photos, and then when we visited it on the ground, we could see that it was undisturbed and in good condition, and [it] was a good choice for excavation.” Similar reasoning guided her team’s choices for subsequent digs as well.
Stonehenge and the pyramids in Giza would not be built for another 3,000 years.
The other recent project, sponsored by the RCU in 2018, took a different approach for its first mustatil excavation, also near AlUla. It was not the best-preserved, explains Wael abu Azizeh, a researcher at the French Institute for the Near East, but it had features suggesting it was well-built and well-organized. Abu Azizeh has led three mustatil excavations in the AlUla region on behalf of Oxford Archaeology while working for the RCU. “Above all, it was chosen because these features were just below an overhang of the cliff rock face, and so protected from rainfall.” This configuration, he says, would have offered optimal preservation conditions for any organic remains.
“This turned out to be verified in the course of the excavation and the unique discoveries we made,” says Abu Azizeh. The first of these was undisturbed deposits of charcoal from two small fires, one flanking each side of an enclosed chamber. The charcoal was later carbon-14 (C14) dated to 5200 BCE—the first-ever firm dating of a mustatil component. Stonehenge and the pyramids in Giza would not be built for another 3,000 years.
Saeed Alahmari was a research archeologist on Abu Azizeh’s excavation. At the RCU’s headquarters in its soon-to-be-renovated building in downtown AlUla, he describes finding several dozen horns of cattle, goat, sheep and ibex in that mustatil’s 3-meter-wide, enclosed chamber, which the team named the Horn Chamber. Speaking through translator and fellow archeologist Paul Mahboub, Alahmari explains that the arrangement of the horns in the chamber showed “meticulous placement,” and that among them, the cattle horns were the first evidence of a domesticated species.
It was “one of the best days of my career,” Alahmari says.
In another mustatil, he continues, the team found “many animal bones and [at a higher level] many human bones, in a specific way that might lead us to the picture that we might have a population there.” Could the mustatil have been a funerary structure?
“They were originally not funerary,” explains Rebecca Foote, RCU’s director of archeology and cultural heritage research. “In their original purpose, there were only horned animal cranial parts placed in the chamber in great numbers in the Horn Chamber of the mustatil Saeed excavated,” Foote adds. “And that C14 date range is about 5300 to 5000 BCE. Then about 4900 to 4800 BCE, the chamber was cut in half and reused for a human burial. So there is evidence of human burials, but it seems to be 100 or 200 years after the original deposit of horns and teeth. All evidence suggests the original use was ritual, and later there was reuse of the site as funerary.”
Kennedy and Thomas’ team has excavated five mustatils since 2019, all in the sandstone canyons east of AlUla. They too have found similar mixes of wild and domestic animal remains as well as similar dates. “We have C14 dates for all the mustatils we have dug, mainly dating the different deposits of animal remains,” says Kennedy. “All fall between about 5200 and 4900 BCE.”
The importance of this mix of wild and domesticated animals appears to be corroborated in the region’s rock art, where scenes of both cattle herding and hunting frequently appear together. Maria Gaugnin specializes in the rock art of northern Saudi Arabia at the Max Planck Institute for the Science of Human History. She points out that this so far seems more coincidence than connection. “I’m not aware of any rock art directly associated with a mustatil,” she says.
After establishing the C14-based ages for the objects discovered, Kennedy began to focus on dates for the structures themselves. For that she turned to optically stimulated luminescence (OSL), which determines when a soil or rock was last exposed to sunlight. She used it to date the time when the people building the mustatil laid its first and lowest course of stones.
“In terms of the connection with the transition to pastoralism, by the time the mustatils were built, pastoralism appears to have been well-established.”
Mustatils and Archeoenigmas
Archeology today is a discipline that, in its science-based form, is only somewhat more than a century old. This makes archeologists only the latest group to try to interpret seemingly inexplicable relics of the past—archeoenigmas—that communities and travelers have for centuries variously lived alongside and discovered for themselves. How and why were the enormous stone heads on Rapa Nui (Easter Island) in the Pacific Ocean created? How about the 2,000-year-old geoglyphs in what is now Peru, known as the Nazca lines? All such archeoenigmas attract both evidence-based speculation as well as more fabulous hypotheses such as aliens, superpowers and lost civilizations. Here are three lesser-known mysteries that, like the mustatils of the Arabian Peninsula, continue to defy interpretation.
The Stone Spheres
In 1940 while clearing jungle in Costa Rica’s Diquis Delta region, the United Fruit Company uncovered numerous partly buried, massive stone spheres. Dated between 500 CE and 1500 CE, around 300 are now known. The largest weighs 16 tons and is more than 2.5 meters in diameter; the smallest is about the size of a basketball. Adding to the puzzle, the source of the stone appears to be more than 80 kilometers away. Firm dating and their purpose remain elusive.
The Plain of Jars
Discovered in the 1930s, the Plain of Jars in the Xiengkhuang Plain of Laos sports at least 3,000 giant stone jars up to 3 meters tall scattered across nearly 100 sites dated from 500 BCE to 500 CE. Archeological investigations over the decades pointed to some consensus that they probably served as burial containers. But the questions persist: Who carved them? Why jars? And why so many?
Discovered in 1993 in southern Turkey, Göbekli Tepe is the world’s oldest known monumental art and the earliest, largest monumental structure associated with a hunter-gatherer way of life. It has multiple concentric rings of massive L-shaped stone pillars carved with scenes of animals both realistic and mythic. Cut into a hill and constructed 11,500 years ago by semi-nomadic hunters centuries before the advent of agriculture, the site was intentionally buried about 1,500 years later. Who constructed it, why, and then, who buried it, and why?
“We have just got some of the OSL dates back,” says Kennedy, “and they appear to match up with the radiocarbon data” of the organic remains. With the structures dated, archeologists could correlate this information with lifeways and knowledge of the climate.
“Northern Arabia 7,000 years ago was very different from today,” states Huw Groucutt, who leads the Extreme Events Research Group at the Max Planck Institute of Geoanthropology. “Rainfall was higher, so much of the area was covered by grassland, and there were scattered lakes. Pastoralist groups thrived in this environment, yet it would have been a challenging place to live, with droughts a constant risk.”
“Mustatils are clearly related to the emergence of pastoral nomadic societies,” says Abu Azizeh. The role of the era’s very gradual climate change, however, remains unclear, although it likely was a factor in determining the species of animals domesticated. “The presence of cattle, for instance, suggests an overall wetter and greener environment,” he says.
“Recent studies suggest that by the Late Neolithic, northwestern Arabia was very arid, but our archeological data doesn’t really suggest this,” says Kennedy. “In terms of the connection with the transition to pastoralism, by the time the mustatils were built, pastoralism appears to have been well-established.”
The environmental changes brought about by the climate changes—desertification—may have led to anxieties about food and subsistence. Groups may have searched for ways to ensure continued abundance, such as rituals that reinforced group bonding and often involved sacrifices.
“The fact that sometimes several of the structures were built right next to each other may suggest that the very act of their construction was a kind of social bonding exercise,” Groucutt writes. And this, he adds, may be a clue as to why there are so many.
“There are so many of them because every community had to build and have its own mustatil ritual monument.”
—Wael Abu Azizeh
Mustatils were not particularly difficult to construct. Using locally available, naturally cleaved sandstone without mortar, a group of 10 people could probably have constructed a mustatil 150 meters long in two to three weeks, according to a recent academic analysis.
Abu Azizeh believes mustatils were a kind of collective or communal monument. “There are so many of them because every community had to build and have its own mustatil ritual monument. In view of the ritual dimension imbued in these structures, I believe the building of a mustatil—involving collective effort and reinforcing social ties—was privileged over reusing a previous mustatil of another clan or group.”
Thomas mostly concurs. “The deposits inside each structure are slightly different—different types of animals or different chambers—so it is highly suggestive of some form of individuality happening with the offerings,” he says. “That may be tribal, different phases of use, different family groups, or different environmental factors that change the preservation.”
Abu Azizeh speculates about one possible scenario: Based on its elongated shape, people would enter and follow a customary, predetermined path. Once the groups had gathered in the space, in effect an open-air courtyard, representatives of the families or clans would enter and successively approach the shrine—the platform-like feature at the mustatil’s end. There two hearths provided light from each side of the low, narrow entrance. Into this intimate space, the individuals would place an offering into the chamber behind the hearths.
Kennedy’s take is similar. “We believe—this is all hypothetical—that you would have seen various communities or groups of people coming together to build the structure. They would then sacrifice the animals that they had brought with them, depositing the cranial elements—like the maxillaries and horns—in the central offering chamber. And then, we believe, there was a big communal feast, with this done as a group bonding experience.”
But it would take only a surprise discovery or two—such as if contemporaneous human remains were to be found alone without associated animal offerings—to prompt significant rethinking. “Our hope is to do more work on these structures in other areas,” says Kennedy.
“It is just about getting more experience,” adds Thomas.
From across the paleolake, under the sky broken only by the blaze of the sun, Kennedy is calling out, “I found something!” She is pointing to a small circle of stones. Thomas records its location. Every discovery is important at this early stage, she says. “Our dream find would be to identify the place where the people who constructed the mustatil were living,” she adds.
Abu Azizeh too is keen to discover traces of similar evidence. “Finding and identifying the occupation campsites of these pastoral nomadic societies, in direct association to the mustatils, would constitute for me a major ‘dream discovery,’” he says.