In the 1920s, during the early days of flight, Royal Air Force pilots crossing the Middle East noticed something bizarre across barren landscape of Syria, eastern Jordan and Saudi Arabia's desert.
The giant structures, which covered the land in their thousands, looked like intricately carved stone wheels, only visible from the sky. Some are pendants. Rings. Others are known as "kites".
Flt Lt Percy Maitland documented the mysterious structures in 1927 for the archaeological journal Antiquity, but they remained largely a secret until the 1970s when Dr David Kennedy, a retired archaeologist at the University of Western Australia, spotted some of them while surveying photographs from Jordan.
"They really dominate the landscape, suggesting a lot of effort was put into constructing these over a huge area," Dr Kennedy said in 2011 of "The Works of the Old Men," of which the structures are called.
Measuring 70 metres wide, Dr Kennedy has been busily studying some of the sites in Jordan from above in planes or helicopters, but its neighbour, Saudi Arabia, has always just been out of his reach. The problem with fully unlocking these secrets for Dr Kennedy was gaining permission to visit the country.
Fast forward to 2017, and Dr Kennedy is using a far simpler method to discover the world's hidden secrets; Google Earth.
In the past 10 years Google Earth has been particularly helpful for probing archaeologists keen to track every inch of the Earth, but notably in the Saudi region.
More than 400 previously undocumented structures - or "gates" as they are called - have been uncovered using the technology, and Dr Kennedy is particularly pleased.
"We tend to think of Saudi Arabia as desert, but in practice there's a huge archaeological treasure trove out there and it needs to be identified and mapped," he told the New York Times.
"You can't see them very well from the ground level, but once you get up a few hundred feet, or with a satellite even higher, they stand out beautifully."
Last month, Dr Kennedy received an invite to investigate the structures from above. Two hundred sites in all across the Harrat Khaybar and Harrat Uwayrid regions. Gates. Kites. Triangles. Bull's eyes. Keyholes. They were all there. And more vivid than Google Earth.
"From 500 feet, you can see the vital details of structures that are invisible in the fuzzy image on Google Earth," he said.
"Once you get out in the desert areas, where you wouldn't expect to find much at all, they are absolutely littered with archaeological sites.
"We're now discovering now is exactly the same in Saudi Arabia."
But what does it all mean? Is there a connection between all these structures? According to Dr Kennedy, the structures are anything but random; in fact, they are quite deliberate.
"We could see immediately they were much more complicated than they appeared on Google Earth," Dr. Kennedy told the New York Times.
"They are much more sophisticated than I was prepared for."
To this day much of the conclusions are still speculation at best, but they are thought to date back as far as 9000 years ago and used by nomadic tribes as traps for hunting and farming.
Dr Kennedy thinks tribes would herb gazelle into the structures where hunters could trap and kill them.
"Essentially there was no escape," said Dr. Kennedy.
The keyholes, on the other hand, could have been used as tombs or ritual buildings to bury the dead.
But the challenge for experts now, is to study them on the ground. And radio carbon testing to sure of time periods. It could be decades until we find the real answer - until then, the Arabian secrets remain buried in the sand.