A mysterious cone-shaped structure that may be an ancient burial site has been found in the Sea of Galilee.
Researchers from Tel Aviv University found the structure deep beneath the surface of the water during a geophysical survey.
It measures 230ft in diameter, is 39ft high and weighs an estimated 60,000 tonnes, Shmuel Marco, one of the researchers, said.
The team believes it was built on dry land around 6,000 years ago but later was submerged beneath rising sea levels.
The findings were published in the Journal of Nautical Archaeology. Marco said that the structure was built according to a very specific construction plan - the stones used were brought from a site over a mile from the where the monument was built.
The team were initially looking to find out the origins of pebbles found in an area of the Sea of Galilee. However, sonar imaging showed a huge pile of stones in what is otherwise a smooth basin.
After inspecting the site, they found it was not just a random build-up of stones, but a purposefully built structure made from basalt.
Yitzhak Paz, of the Antiquities Authority and Ben-Gurion University, said the structure is similar to early burial sites found in Europe and was probably built during the start of the Bronze Age.
He also said the structure could have been linked to Beit Yerah, a nearby ancient city that was the largest in the area at the time.
Researchers also looked to date the structure by examining the accumulation of sand around the base - the build-up is now six to ten feet below the bottom of the Sea of Galilee, suggesting it is several thousands of years old.
Marco said the area the structure is built on is tectonically active, so it may have shifted over time, rather than water levels rising to submerge it: "The base of the structure - which was once on dry land -- is lower than any water level that we know of in the ancient Sea of Galilee. But this doesn't necessarily mean that water levels have been steadily rising."
The team also say it is possible the structure built underwater as an ancient fishery - the authors wrote: "A possible interpretation for the structure is related to the fact that it attracts ﬁsh and thus may be interpreted as a part of a marine-based economy. If so, the structure must have been built as an underwater structure.
"Stone-built installations that are thought to be ancient ﬁsh nurseries are well known in the Sea of Galilee. They are found near the shores at regular intervals. They were generally made of basalt pebbles and cobbles up to one foot long, piled to form circular installations.
"Their date is not clear. However, they are signiﬁcantly smaller than the structure we discuss here, with diameters between five and 13ft and heights up to two feet."
The team now plans to learn more about the origin of the structure and look for artefacts that will more accurately date it and provide clues about its purpose.