The discovery of an almost perfectly preserved pottery vessel from the bottom of Lake Biwa has opened up a new chapter in the study of Japan’s prehistoric past. Unearthed in October 2025 from the Tsuzuraozaki (also spelt Tsuzura-Ozaki or Tsuzura Ozaki) underwater ruins, the vessel dates back more than 10,000 years and is considered one of the oldest known pottery artefacts in the world. Its remarkable preservation, combined with the advanced technology used to retrieve it, has transformed this finding into a landmark moment in underwater archaeology. The discovery also sheds new light on the early Jomon-period societies and their evolving ceramic traditions, allowing scholars to extend their understanding of the ancient craftsmanship and cultural life in prehistoric Japan.
About the Discovery and the Site
At a depth of 64 metres, researchers retrieved a nearly-intact pottery vessel shaped like an artillery shell, measuring about 25 centimetres in height. The artefact was located in an area long believed to hold the secrets of Japan’s ancient lakeside communities. Since 1924, when fishermen accidentally dredged up the ancient pottery in their nets, the Tsuzuraozaki site has intrigued archaeologists. Over the decades, more than 200 pottery fragments have been recovered from the area, yet the depth and difficult conditions have impeded the systematic exploration. The newly recovered vessel, found upright and intact, stands out as the oldest artefact ever recovered from the site and provides an unprecedented opportunity to understand the context of these underwater ruins.
The exceptional site of preservation is attributed to Lake Biwa’s geological characteristics. The site lies in a valley-like depression where sediment accumulation is minimal. Ongoing tectonic movements have helped keep the lakebed exposed, ensuring that the artefacts remain in situ for thousands of years. This unique combination of environmental conditions has allowed the vessel to remain untouched for more than 10,000 years, unlike many land-based artifacts that often suffer fragmentation and erosion.
Insights into the Early Jomon-Pottery Traditions
The vessel is believed to belong to either the Jinguji-style or Konami Upper-layer tradition of the early Jomon-period pottery. These traditions represent some of the humanity’s earliest experiments with fired clay and mark a significant turning point in prehistoric cultural development. The Jinguji-style pottery is distinguished by pointed bases, soft contours, and engraved patterns. These traits reveal a growing interest in both the utilitarian and aesthetic functions of ceramic objects. The Konami Upper-layer style, on the other hand, is associated with refined surface treatments, linear decorative motifs, and improved firing techniques that point to the technological advancements in the Early Jomon Period.
The vessel’s characteristics align with the roots in the critical transitional phase. Its pointed base and engraved patterns align with the ceramic conventions of both the traditions, suggesting a cultural environment in which pottery no longer served purely functional purposes. Instead, it became a medium through which symbolic, artistic, and social meanings were expressed. This shift represents a crucial stage in Japan’s prehistoric past, revealing the evolving sense of identity and creative expression of the early communities.
How Technology Enabled the Discovery
The retrieval of the ancient vessel was made possible through the use of state-of-the-art technology. Researchers employed a 3-D underwater scanning system, originally developed for submarine cable inspection. Equipped with four synchronised cameras, the system generated a detailed reconstruction of the 1,200-by-40-metre lakebed area. Despite the murky waters of Lake Biwa, the scanning produced documentation comparable to diver-led surveys. These technological capabilities enabled the exploration of depths previously inaccessible to traditional archaeological methods.
Complementing the scanning system, sophisticated autonomous underwater vehicles (AUVs) were developed by Japan’s National Maritime Research Institute. Originally designed for deep-sea exploration, these AUVs feature advanced formation control systems, high-resolution sonar, and autonomous navigation mechanisms, which have proven effective in real-world missions, such as multivehicle coordination and deep-water archaeological searches. In the earlier exploration of Lake Biwa, the hovering AUV ‘Hobalin’ was used to locate the ancient artefacts. The same technological principles—precise control, stable manoeuvring, and high-fidelity seabed imaging—were key to the success of the current mission.
Researchers have emphasised that the underwater environment at depths exceeding 30 metres presents significant challenges. However, the integrated use of AUVs and 3-D scanning ushered in a new era of underwater archaeology. This technological revolution not only enhances safety, but also increases the accuracy in documenting the submerged sites. The Lake Biwa discovery demonstrates how robotics and artificial intelligence are reshaping the archaeological methodology and expanding the potential for future findings across Japan’s numerous underwater sites.
Condition of the Vessel
One of the most remarkable features of the discovered vessel is its pristine condition, despite its age. Underwater artefacts remain better preserved due to stable conditions that shield them from exposure, erosion, and human intervention. At Tsuzuraozaki, the minimal sediment accumulation and stable geological structure significantly contribute to this preservation. This geological setting ensures that the artefacts, whether Jomon ceramics or later objects, remain intact for many centuries.
The discovery also coincides with the documentation of six haji pottery jars from the middle of the Kofun Period, roughly 1500 years old, found nearby. While much younger than the Jomon vessel, their presence reveals the layered history of human activity in the region and underscores the long-standing relationship between the local communities and Lake Biwa. These findings indicate that the lake area has been an important cultural and possibly the spiritual site across multiple historical periods.
Unravelling the Mysteries of the Underwater Ruins
Scholars continue to debate the origins and significance of the Tsuzuraozaki underwater ruins. Several theories attempt to explain how so many artefacts came to rest in the depths of Lake Biwa. Some theories presume that the area once supported the lakeside settlements that were gradually lost to subsidence or earthquake-related land shifts. Others suggest that rising water levels over centuries may have submerged the ancient fishing communities. Another theory proposes ritualistic deposition, in which pottery vessels were intentionally placed into the lake as part of ceremonial practices.
The newly recovered vessel, found upright and intact, offers rare contextual clues that may help resolve these longstanding debates. Its condition and placement suggest that it may not have been simply abandoned or accidentally lost. Instead, it could have been a part of a larger cultural practice whose meaning has been obscured by time. Additionally, the discovery encourages further research into the spiritual and cultural lives of early Jomon societies whose customs remain partly shrouded in mystery.
A Turning Point for Underwater Archaeology
This discovery symbolises a significant shift in the archaeological practice. With nearly 400 underwater archaeological sites across Japan, the integration of robotics, advanced sonar systems, and high-resolution scanning promises to accelerate the pace of discoveries. The combination of cutting-edge technology and traditional archaeological expertise is transforming the study of Japan’s ancient past, enabling the researchers to uncover artifacts that were once inaccessible. This discovery not only extends the timeline of ceramic craftmanship in the region, but also demonstrates how innovations in underwater exploration could reveal new dimensions of prehistoric culture.
The vessel’s age, condition, and cultural importance make it a key artefact in understanding the early Jomon period. The discovery highlights the sophistication of prehistoric Japanese societies and enriches the current knowledge of their evolving technologies and artistic expressions. At the same time, the discovery reinforces Lake Biwa’s status as a site of immense archaeological potential, offering a rare window into the deep past.
About Lake Biwa
Lake Biwa, covering an area of 670.25 square kilometres with a catchment area of 3,174 square kilometres, is one of the world’s few ancient lakes with a continuous history, stretching back about one million years. Its north basin reaches a maximum depth of 104 metres, while its south basin is much shallower, at eight metres. The lake sustains 14 million people through its outflowing river system and supports commercial fishing with ayu (Plecoglossus altivelis) as a key species.
This lake is recognised as a quasi-national park, a wildlife sanctuary, and a Ramsar wetland of international importance. With more than 3,100 recorded species and 62 confirmed endemics, Lake Biwa holds immense ecological value. Its long geological history and biodiversity makes it both a natural treasure and a crucial habitat that continues to shape the cultural and the environmental landscape of Japan.
Conclusion
To conclude, the discovery of this ancient artefact, nestled within the cultural and ecological landscape of Lake Biwa promises to unlock further secrets about the earliest civilisations of Japan. Also, the exact purpose of the site remains a mystery. Further investigation is expected to reveal the kind of daily lives and cultural practices of the Early Jomon-period people.
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