The eleven "Big Circles" in Jordan are each about 1,300 feet in diameter.
Researcher David Kennedy, who has led the Aerial Archaeology in Jordan Project since 1997, told Live Science that the circles' similarity is "too close to be a coincidence." The archaeologists are studying high-resolution aerial images of the stone circles, which provide details about structures that have been "shrouded in mystery for decades," Live Science notes.
The circles were created with low stone walls that are just a few feet high. The circles apparently didn't contain gates or openings, so people visiting the inside of the circles would need to "hop over the walls," according to Live Science.
The Big Circles were first seen in the 1920s, but they haven't been studied to much extent, and researchers still don't know when or why they were built. Archaeologists suspect that the circles are at least 2,000 years old, but they could be much older than that — even as old as prehistoric time periods. Kennedy told Live Science that archaeologists will need to "conduct more actual fieldwork" to solve the circles' mystery.