About 400 mysterious stone structures, dating back thousands of years, have been discovered in Saudi Arabia thanks to satellite images on Google Earth.

For the time being, archaeologists are unaware of the exact purpose of the structures found in Saudi Arabia with the aid of satellite imagery. It is believed that the ancient stone structures could go be around 7,000 years old.

Different types of stone structures have also been discovered in Saudi Arabia. Some stone structures are built on top of or even inside gates. This suggests that the gates are older than the other stone structures.

According to reports from Live Science, groups of stone walls – called “gates” by archaeologists, because they look like field gates from above – have been detected in a region known as Harrat Khaybar. Some of these “gates” are located next to a volcanic dome that at one time spewed out basaltic lava.

The gates “are stone-built, the walls roughly made and low,” David Kennedy, a professor at the University of Western Australia, wrote in a paper set to be published in the November issue of the journal Arabian Archaeology and Epigraphy. The gates “appear to be the oldest man-made structures in the landscape,” Kennedy noted, adding that “no obvious explanation of their purpose can be discerned.”

This picture of the lava dome that has gates on it was taken in the 1980s by Vic Camp. The taller lava dome behind it is called “Jabal Abyad” a name which means “white mountain” in Arabic. The lava domes are no longer active although in the past basalt lava poured from them.

The smallest of these strcutures—gates—extends around 13 meters while the longest one stretches out for a staggering 518 meters in length.

As noted by Live Science, many have multiple stone walls that, in some instances, form a rectangular design; some of the others, called “I” type gates, have only one stone wall with heaps of stone at each end.

“Gates are found almost exclusively in bleak, inhospitable lava fields with scant water or vegetation, places seemingly amongst the most unwelcoming to our species,” Kennedy wrote.

Most of the structures were discovered through satellite inspection, and no archaeological fieldwork was yet carried out.

The gates come in a number of different shapes and sizes.

In order to determine the exact nature and origin of the enigmatic gates, archaeological fieldwork is a must do.

In the 1980’s before the gates were discovered, volcanologists Vic Camp and John Roobolmapped an area of the Harrat Khaybar that included a lava dome festooned with gates and other stone structures notes Live Science.

Since the Lava Domes are no longer active, fieldwork shouldn0t be hard to perform.

“We see several areas where the younger lavas are devoid of such [stone] structures, although surrounded by several [stone structures],” Camp told Live Science. One of the stone structures is partially covered in hardened lava, photographs show. Camp estimates that some of the gates around the lava dome were built around 7,000 years ago.

(H/T LiveScience)