University of Western Australia archaeologist David Kennedy has spent decades looking for ancient stone structures known as "The Works of Old Men" that dot the rugged harrats, or lava fields, of Saudi Arabia and Jordan. But it wasn't until he could look down from above that he could really see them.

Using Google Earth, Kennedy has identified nearly 400 previously undocumented examples of these ancient stone edifices across the Saudi Arabian desert. The structures, which Kennedy says resemble "gates," hint at a once-extensive but mysterious culture that built them some 2,000 to 9,000 years ago, reports Phys.org.

"I refer to them as Gates because when you view them from above they look like a simple field gate lying flat, two upright posts on the sides, connected by one or more long bars," he said. "They don't look like structures where people would have lived nor do they look like animal traps or for disposing of dead bodies. It's a mystery as to what their purpose would have been."

Impossible to see from the ground level

These vast structures have remained hidden in part because they are very difficult to see from the ground. These vast structures have remained hidden in part because they are very difficult to see from the ground. (Photo: APAAME/David Kennedy/Twitter)

The reason these vast structures have remained hidden for so long is due in part to the barren mountains and desert that make up the terrain, but also because they are incredibly difficult to spot from the ground.

"You can't see them in any intelligible way at the ground level, but once you get up a few hundred feet, or with a satellite even higher, they stand out beautifully," explained Kennedy.

Kennedy established the Aerial Photographic Archive for Archaeology in the Middle East (APAAME) in 1978, mostly from his efforts to locate these archaeological sites via helicopter. He has also jointly directed the Aerial Archaeology in Jordan (AAJ) project since 1997. Modern day technology, such as satellite and drone surveillance, opens up possibilities for aerial exploration, however.

The shapes of Kennedy's so-called Gates range from giant circles of stone, some of which are 400 meters across, to Kites (animal traps), Pendants (funerary monuments), and Wheels (unknown). Though referred to as "Works of Old Men" by the modern-day Beduin people, it's unclear whether the ancient structures were truly built by Beduin ancestors. Their origin is truly mysterious.

Now that the sites have been identified, the next step will be to visit them up close, perform excavations, and get to the bottom of how and why they were created, and by whom.

Kennedy's findings will be described in a research paper to be published in the journal Arabian Archaeology and Epigraphy.

Editor's note: This story has been updated since it was originally published in October 2017.