Of all the Stoneworks of Asuka, the Rock Ship of Masuda is the most unusual and largest of all. Image credit: Saigen Jiro/Wikimedia Commons (CC0 1.0)

In the quiet hills of Japan, the “Rock Ship of Masuda” can be found hidden among the bamboo looking as if it’s just crash-landed from another planet. Despite its strangely smooth surfaces and angular indents, the structure has been around for centuries, although its original purpose has been long-forgotten.

Bar the odd tourist blog, very little information about the strange stone is published in English. It’s located just a 15-minute walk from Okadera Station on a forested hill near an elementary school in Kashihara, Nara Prefecture.

The area is known for its carved granite stones, many of which are fashioned into the shape of human-like figures and animals. It’s uncertain when they were made, but some have argued they were built around the 7th century CE towards the end of the Kofun period.

Collectively, the artworks are known as the Stoneworks of Asuka. They’re particularly interesting as they stand in contrast to the dominant style of Buddhist art that swept through Japan at the time.

North side of the granite structure. Image credit: Saigen Jiro/Wikimedia Commons (CC0 1.0)

The Rock Ship of Masuda, aka Masuda-no-iwafune, is the most unusual and large of them all. The carved stone measures 11 meters (36 feet) in length, 8 meters (26 feet) in width, and 4.7 meters (15 feet) in height – roughly comparable to the size of a luxury tour bus.

Its unusual shape and size are especially impressive when you realize it was made out of granite, a notoriously tough rock that’s extremely difficult to cut and carve. Along with the square cut indents on top of the rock, it also features a square scale-like pattern on the side that’s also been intentionally carved.

People have dreamt up a few theories about why the rock was carved. As is often the case with unexplained archeological finds, some have speculated it was used for star gazing and astronomy. A more likely explanation is that it played some kind of spiritual function, perhaps relating to the burial or celebration of the death.

Truth be told, however, the story of the Rock Ship of Masuda is still largely a mystery.