A group of 19 "keyholes" at Al Wadi, in the Saudi Arabian desert, observed by archaeologist David Kennedy from a helicopter. Dr. Kennedy took more than 6,000 aerial photographs of these mysterious, ancient structures.Credit...David Kennedy For nearly a decade, David Kennedy marveled from behind his computer screen at thousands of mysterious stone structures scattered across Saudi Arabia’s desert.
![A Close-Up on Mysteries Made of Stone in Saudi Arabia’s Desert - The New York Times](https://cdn-ak-scissors.b.st-hatena.com/image/square/ac0a18297d31bcdea24b706fde16c6869164efc0/height=288;version=1;width=512/https%3A%2F%2Fstatic01.nyt.com%2Fimages%2F2017%2F11%2F18%2Fscience%2F18GATES1%2F18GATES1-facebookJumbo.jpg%3Fyear%3D2017%26h%3D550%26w%3D1050%26s%3D1616c5459664b02e964e1dc8c84ad2ca83602cc81b5adf2b3c550524522ece88%26k%3DZQJBKqZ0VN)