These stone-structures, dating back thousand of years and are known as “gates” by the archaeologists (because they resemble field gates from above), were found in clusters in a region in west-central Saudi Arabia called Harrat Khaybar. So far, the archaeologists aren’ t sure of the purpose of the gates or the exact age of these structures.
“Gates are found almost exclusively in bleak, inhospitable lava fields with scant water or vegetation, places seemingly amongst the most unwelcoming to our species.” Some of the “gates” are actually located on the side of a volcanic dome that once spewed basaltic lava. One of the stone structures is partially covered in hardened lava, photographs show. According to David Kennedy, a professor at the University of Western Australia, the gates “are stone-built, the walls roughly made and low.” He also added that “no obvious explanation of their purpose can be discerned.” More Infos at livescience.com