An underwater photo shows part of the monumental structure, which is made… (Shmuel Marco / International…)
Archaeologists in Israel have discovered a mysterious stone monument weighing 60,000 tons and rising 32 feet above the bottom of the Sea of Galilee.
Scientists don't know who built the structure, or why, but in a recent paper in the International Journal of Nautical Archaeology the researchers shared a few hypotheses before concluding that further study is needed.
The mystery rock pile was first discovered in 2003 during a sonar survey of the bottom of the southwestern part of the sea. The sonar revealed a pile of boulders arranged in a circular shape, lying on the sea floor.
The structure, which cannot be seen from land, is massive -- about twice the diameter of Stonehenge.
Further study by a team of scuba-diving investigators revealed that the boulders are made of basalt and have no decorative chiseling or cutting. Individual boulders are as big as 3 feet across, and the lower half of the structure is covered by sand.
They also noted that nothing was growing on the boulders and that the rocky area was teeming with tilapia, which may like using the rocky crevices to hide in.
Because nothing about the structure occurs naturally anywhere else in the sea, researchers have conlcuded it is man-made. In an interview with LiveScience, Yitzhak Paz of the Israel Antiquities Authority, one of the researchers on the paper, said the structure could date back more than 4,000 years.
"The more logical possibility is that it belongs to the third millennium B.C., because there are other megalithic phenomena [from that time] that are found close by," Paz said, noting that those sites are associated with fortified settlements.
So what is this thing? Scientists have a couple of theories.
One is that it may be a type of ancient fishery, in which the rocks were dropped into place to create a gathering place for fish. Stone installations that are believed to be fish nurseries are well documented in the Sea of Galilee, the scientists noted, although none of those comes close to the mystery structure in size.
Alternatively, the structure may have been built on land when the water level was lower than it is today. Similar, smaller stone structures are found at nearby prehistoric sites.
Further study is clearly needed before we get to the bottom of this mystery.