Get the full EPUB
The EPUB is part of the HistorIQly Plus library. The case file on this page stays free to read.
This EPUB is already in your library. The case file on this page stays free to read.
Download EPUBPlus includes every book in the library. See what Plus includes
Every book in the library is yours to download.
All EPUBs are in English. Translations are coming.
Off the southern coast of Japan's westernmost island lies an enormous stepped rock formation. Flat terraces and sharp edges give it an architectural appearance, while its sandstone layers and fractures offer a natural explanation.
Discovered by a dive operator scouting for hammerhead sharks in 1986, the Yonaguni Monument has been called everything from a ten-thousand-year-old temple to a striking example of natural geology. Human modification remains unproved; the main formation is consistent with local geology.
~100m Long
Japan’s national tourism organisation describes a core about 100 metres long, 60 metres wide and 25 metres high. Measurements differ with the boundaries assigned to the wider formation.
Aratake
Kihachiro Aratake, a dive operator scouting for hammerhead sharks, stumbled upon the formation in the warm, clear waters off Yonaguni's southern coast.
Since 1986
Since 1986, scientists have argued over whether the monument is a natural geological formation, a human construction, or something in between.
None
No securely associated archaeological assemblage has established the formation as a constructed settlement. Reported objects from the wider area need context before they can demonstrate work on these terraces.
The Evidence
The Steps
Broad, flat terraces descend from the top of the structure to its base like a colossal staircase. Their regularity has been cited as evidence of human construction — and as a textbook example of natural sandstone erosion.
The Sanninudai Problem
Stepped outcrops above the waterline display bedding, joints and erosion that help explain the underwater geometry. Kimura also claimed human work at some onshore sites; the geological comparison does not depend on universal agreement.
The Twin Megaliths
Two massive rectangular stones stand side by side, their resemblance to standing stones found at megalithic sites worldwide impossible to ignore — and equally impossible to prove meaningful.
The Investigation
Discovery
Dive operator Kihachiro Aratake discovers the monument while scouting for hammerhead sharks off Yonaguni's southern coast.
The Professor
Masaaki Kimura of the University of the Ryukyus makes his first dive. He becomes convinced the monument is at least partly man-made.
The Sceptic
Boston University geologist Robert Schoch examines the site and concludes it is most likely natural — but leaves the door open for possible human modification.
The Science
Ogata, Otsubo and Itoh publish a study of Yonaguni’s onshore geosites, describing coastal erosion, rock contrasts, faults and joints. It supplies geological context, rather than a direct archaeological test of underwater carving.
The Protagonists
Masaaki Kimura
University of the RyukyusMarine geologist who surveyed the formation and argued for human modification. He interpreted marks and platforms as carvings and structures; those identifications remain disputed.
Robert Schoch
Boston UniversityGeologist who examined the monument and concluded the stepped terraces were consistent with natural erosion of jointed sandstone — the same processes that shaped Yonaguni's coastline.
The Question That Won't Die
The monument’s major terraces are consistent with naturally layered and fractured sandstone. Claims of limited human alteration remain unproved, and require evidence tied to particular surfaces.
Geological surveys and preliminary archaeological observations have examined the island and its surrounding waters. They have not established the stepped formation as an ancient constructed city.
Get the Full Book
10 chapters tracing Aratake’s discovery, the sandstone geology, proposed modifications and the evidence behind the debate.