These 10,000 Year-Old Sunken Ancient Ruins in Japan Remain a Huge Mystery

There's a mysterious 10,000-year-old massive underwater monument off the coast of Japan. 

It's called the Yonaguni Monument, located off the coast of Yonaguni, the southernmost of the Ryukyu Islands, and scholars have yet to figure out whether it's man-made or natural. 

But an expert told National Geographic the structures found in the monument by divers suggest it was man-made in Asian culture. 

"The characters and animal monuments in the water, which I have been able to partially recover in my laboratory, suggest the culture comes from the Asian continent," he said.

Experts have discovered 10 distinct structures in the area that could be ruins of an ancient city. 

Decades of research by scuba divers shows the sunken city likely submerged at once during a massive earthquake of sorts.

Divers have found evidence of ruins of a castle, triumphal arch, five temples and a stadium.

They call it the "Japanese Atlantis."

Dr. Robert M. Schoch, a Boston University professor who's conducted field research at ancient sites in Egypt as well, believes it could be a natural formation. "We should also consider the possibility that the Yonaguni Monument is fundamentally a natural structure that was used, enhanced, and modified by humans in ancient times," he wrote in his book Voices of the Rocks.

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