Harrat Khaybar
Harrat Khaybar is a volcanic field located in the north of Medina in Saudi ArabiaNASA

Hundreds of huge and mysterious stone structures have been found on old lava domes in a remote desert in Saudi Arabia. Australian archaeologist David Kennedy has discovered around 400 such mysterious stones using Google Earth.

The structures dating back thousands of years are located in the volcanic field of Harrat Khaybar, north of Medina in Saudi Arabia. The formations are called the "gates" because they look like old-fashioned barred gates from above.

The gates "are stone-built, the walls roughly made and low," Kennedy wrote in his paper, which will appear in the November issue of Arabian Archaeology and Epigraphy. "The gates appear to be the oldest man-made structures in the landscape," he mentioned in his paper.

"Identification, mapping and preliminary interpretation imply an early date in the sequence of the works—perhaps the very earliest—but no obvious explanation of their purpose can be discerned," he wrote.

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

These structures differ in size. The smallest gate extends about 43 feet (13 meters), while the longest measures 1,699 feet (518 m). The gates were discovered through satellite surveys and they look similar to structures that are found in the Middle East.

Other prominently studied structures are "kites," which were animal traps, and "wheels." These structures are often found on top of the gates, suggesting the gates pre-date the stone structures.

"The Works known as Kites—which are certainly animal traps, may be as old as 9,000 years before present in some cases and there is one example of a Kite overlying a Gate—i.e. the Gate is older. So Gates may be up to or more than 9,000 years old, which takes one back to the Neolithic (Age)," Kennedy told Newsweek.

Kennedy said that archaeological fieldwork is required to find out when exactly the gates were constructed.