By YASUJI NAGAI/ Staff Writer
September 10, 2025 at 18:17 JST
In a potential archaeological breakthrough, a remarkably preserved piece of ancient pottery has been spotted on the floor of Lake Biwako, shedding new light on ritual practices associated with a mysterious underwater site.
Researchers captured video footage of the lakebed at a depth of 70 meters, revealing what appears to be a stemmed bowl lying undisturbed, along with a possible shallow dish nearby.
The discovery was made on July 2, using a remotely operated underwater vehicle deployed by the Biwako Trust, a nonprofit organization dedicated to protecting the environment of Japan’s largest freshwater lake in Shiga Prefecture.
Michio Kumagai, Biwako Trust executive and senior researcher at Ritsumeikan University, led the team, exploring an area 200 to 300 meters off the Tsuzuraozaki Cape in the northern part of the lake.
Based on its shape, the stemmed bowl is believed to date to the fifth century, according to Sadakatsu Kunitake, chief archaeologist at the Nara National Research Institute for Cultural Properties.
“It is astonishing that a more than 1,500-year-old clay vessel remained nearly intact, like a time capsule emerging from the deep,” said Kunitake.
He added that the bowl’s design suggests it was used in rituals, reinforcing the connection between the site and ceremonial practices.
This is the first time a ritual vessel has been identified at the site, according to Kumagai, who believes the lakebed may still be hiding many more artifacts.
The Tsuzuraozaki underwater ruins were first discovered in 1924, when prehistoric pottery became entangled in fishing nets.
Since then, approximately 200 artifacts--dating from around 10,000 to 1,000 years ago--have been recovered from depths of 10 to 70 meters.
Various theories explain why so many artifacts ended up at the bottom of Lake Biwako, including that clay pieces were dropped into the lake as part of rituals, sank with boats in accidents or were left behind when an ancient community was submerged due to geological changes.
The recent discovery may help solve an archaeological mystery that has long baffled researchers.
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A stemmed bowl believed to have been used for rituals in the fifth century is discovered on July 2 on the bottom of Lake Biwako in Shiga Prefecture, at a depth of 70 meters. (Provided by Biwako Trust)
