Ancient Urn Discovered by Robot at Bottom of Japan's Biggest Lake Mystifies Archaeologists

Lake Biwako, near Kyoto, in central Japan. A robot has photographed a nearly intact ancient urn at the bottom of Japan’s largest freshwater lake. Public Domain Pictures

A robot has photographed a nearly intact ancient urn at the bottom of Japan's largest freshwater lake, according to Japanese national paper the Asahi Shimbun. Over the last century, a number of pottery pieces representing a huge range in timeline have been recovered from Lake Biwako, in central Japan. Archaeologists have no idea why.

This urn is an example of Haji pottery, earthenware characterized by a rusty reddish-brown color that came from being baked. (Exposure to fire oxidizes the minerals.) It measures roughly 12 to 16 inches tall, with the opening at the top measuring roughly 8 inches across, and it likely dates to the seventh or eighth century, according to the newspaper Asahi Shimbun. That places it from some point between the Asuka and Nara periods, which lasted from 592 A.D. to 710 A.D. and 710 A.D. to 784 A.D., respectively.

Experts bowled over by ancient #urn found on bed of Lake #Biwako:The Asahi Shimbun #Japan #archaeology

— Asahi Shimbun AJW (@AJWasahi) December 27, 2017

The urn lies in the lake's northern end, in an underwater archaeological site known as Tsuzuraozaki Kotei Iseki. Lake Biwako exhibits a strong current, particularly around where the urn was found, which might be why it was exposed. The current also means the site is easier to explore via robot rather than with human divers, according to the Asahi Shimbun. The team in charge of the robot was led by Kenichi Yano, a professor of archaeology at Ritsumeikan University.

Haji ceramics succeeded the style and techniques of the Jōmon period (an era from the Japanese Neolithic period known for its production of the region's first ceramics), according to the Museum of Oriental Ceramics, Osaka. Around the fifth century, new techniques that traveled from the Korean Peninsula gave rise to Sue pottery, a simpler interpretation of Korean styles, according to Tufts University—several shallow bowls discovered in half a dozen sites near the urn are believed to be examples of Sue earthenware.

Since the 1920s, pottery and fragments of pottery have been discovered at the site dating from the Jōmon period, which lasted from 8,000 B.C. to 300 B.C., all the way up to the Heian period, which spanned 794 A.D. to 1185 A.D., according to the Asahi Shimbun. Archaeologists haven't yet been able to explain why; the artifacts often turn up in fishing nets, from depths ranging from about 30 feet to more than 200 feet. It's possible that the lake was once the site of a settlement that eventually became submerged, or that the ceramics were deliberately sunk in "obscure rituals," according to the Asahi Shimbun. Or it's possible the lake was just used as a dumping ground.