Named after the Arabic word for rectangle, mustatil structures were first discovered in the 1970s, but received little attention from researchers at the time. Hugh Thomas at the University of Western Australia in Perth and his team wanted to learn more about them, and embarked on the largest investigation of the structures to date.
Using helicopters to fly over north-west Saudi Arabia and then following up with ground explorations, the researchers found more than 1000 mustatils across 200,000 square kilometres – twice as many as were previously thought to exist in this area. “You don’t get a full understanding of the scale of the structures until you’re there,” says Thomas.
Made from piled-up blocks of sandstone, some of which weighed more than 500 kilograms, mustatils ranged from 20 metres to more than 600 metres in length, but their walls stood only 1.2 metres high. “It’s not designed to keep anything in, but to demarcate the space that is clearly an area that needs to be isolated,” says Thomas.
In a typical mustatil, long walls surround a central courtyard, with a distinctive rubble platform, or “head”, at one end and entryways at the opposite end. Some entrances were blocked by stones, suggesting they could have been decommissioned after use.
Excavations at one mustatil showed that the centre of the head contained a chamber within which there were fragments of cattle horns and skulls. The cattle fragments may have been presented as offerings, suggesting mustatils may have been used for rituals.