In the 1920s, a mustachioed British commander named Lionel Rees set out across the deserts of what would become Jordan. Snapping some of the earliest archaeological aerial photographs, he observed numerous immense, nearly perfect stone circles. “All three are almost exact circles, are different from anything else in the country,” he wrote in the journal Antiquity.

Rees was baffled by the circles, some of which were 1,200 feet in diameter. But despite their enigmatic nature, his findings were all but ignored. “It was 60 years before anyone noticed [the circles] again, and only in the last 10 years have we started flying over every bit of the country looking for more,” archaeologist David Kennedy told The Washington Post.

As first reported by Live Science, what Kennedy found surprised him. There were more giant stone circles, many more, than they had known. They were made of rock and about a meter in height. In all, he found 12 circles in Jordan, another in Syria and two more in southeastern Turkey. Despite the distance separating the circles, they’re strikingly similar, said Kennedy, the archaeologist for the Aerial Photographic Archive For Archaeology in the Middle East.

Where did they come from? What purpose did they serve and for whom? “I can’t even pretend to know what the answers are,” he said.

Adding onto research Kennedy last year published in the German journal, Zeitschrift fur Orient Archaologie, he has now snapped a series of high-resolution, striking images that lay bare the structures’ intricacies and similarities but do nothing to solve their mysteries. It’s unclear how old they are, Kennedy said. They’re likely older than the Roman Empire, as an ancient Roman road runs across one of them. “They could even be prehistoric,” he said.

The Middle East, Kennedy wrote in his study, is “thickly strewn” with circular structures, but most are significantly smaller than the ones he has uncovered. “Few of these Big Circles have ever been explored on the ground; fewer still in any detail,” the article stated. “It has been rare for such reportage as exists to say much about their form, character, associations and date. Now, however, [this] has led to the photographing of 11 of those in Jordan.”

One of the more starting aspects of the “Big Circles”: They exist in nearly every environment. Some emerged in the desert. Others in craggy terrain. More were near hills. “These enigmatic sites seemed until very recently to be confined to Jordan,” the paper said. “The unexpected discovery of one Circle to Syria, 300+km from those in Jordan is a warning…. It is possible further examples will be found.”

Kennedy doesn’t think the circles were the creations of some ancient, not-yet-discovered civilization, but the manifestation of an as-yet unexplained cultural practice. “These are not natural things,” he said. “Occasionally we have found artifacts nearby…. They can’t just be a coincidence. There’s some purpose behind it. But we can’t figure out what it is.”