Iwajuku Ruins is a Paleolithic archaeological site located in Asami, Kasakake Town, Midori City, Gunma Prefecture. Designated as a National Historic Site, it is one of the most important archaeological discoveries in Japan because it fundamentally changed understanding of the history of human settlement in the Japanese Archipelago.
Before the discovery of Iwajuku, it was widely believed that people had not lived in Japan before the Jōmon Period. Discoveries at Iwajuku, however, provided evidence that humans had been living in the Japanese Archipelago more than 30,000 years ago, long before the Jōmon Period.
This discovery became a major turning point in the history of Japanese archaeology and pushed the known history of human activity in Japan back by tens of thousands of years.
Around 1946, amateur archaeologist Chūyō Aizawa discovered chipped stone tools in a layer of reddish soil known as the Kanto Loam Layer.
At the time, archaeological research generally regarded the loam layer as natural ground and rarely investigated the layers beneath it. The Jōmon culture was widely considered to represent the oldest known culture in Japan.
Aizawa, however, continued his investigations because he believed that his discovery was significant. In 1949, he conducted an excavation together with a research team from Meiji University.
The excavation uncovered clearly man-made stone tools within the Kanto Loam Layer, providing archaeological evidence that a Paleolithic culture had existed in Japan.
Excavations at Iwajuku revealed two different stone tool cultures located in separate archaeological layers.
The lower layer, known as Iwajuku I Culture, dates to approximately 30,000 years ago, while the upper Iwajuku II Culture is thought to date to approximately 20,000 years ago.
Artifacts from the Iwajuku I Culture include chipped stone axes and scrapers made from shale. Charred material was also discovered, suggesting that the people living here may have made use of plant resources.
The Iwajuku II Culture produced a variety of stone tools, including knife-shaped tools made from materials such as obsidian and agate. These artifacts provide evidence of developments in stone-working technology over time.
Iwajuku Ruins therefore represent more than a single moment in prehistoric history. They provide important evidence of cultural changes over a long period of human activity.
The period represented by these discoveries is generally known as the Paleolithic Period or Pre-Pottery Period in Japan.
At the Iwajuku Museum, however, the term “Iwajuku Period” is also used to emphasize the distinctive cultural characteristics of prehistoric Japan. It refers to an early period when people lived without pottery and depended largely on hunting and gathering.
Following the discovery at Iwajuku, archaeological sites from the same period were identified throughout Japan. Today, more than 10,000 Paleolithic sites have been documented across the country.
Iwajuku is regarded as the discovery that opened the way to systematic research into this earliest period of human history in Japan.
Next to the archaeological site is the Iwajuku Museum, where visitors can learn about the stone tools discovered at the site, the history of its excavation, and the natural environment in which prehistoric people lived.
The museum features a full-size replica of a mammoth skeleton, offering visitors a sense of the dramatic environment of the Ice Age. Displays also include an aurochs-like giant deer skull and exhibits explaining the process of making stone tools.
The museum is designed to make prehistoric archaeology accessible to visitors of all ages, including families with children.
At Site B of the Iwajuku Ruins is the Iwajuku Dome, officially known as the Historic Site Iwajuku Ruins Archaeological Remains Preservation and Observation Facility.
Inside the dome, visitors can observe an actual cross-section of the Kanto Loam Layer. Multimedia explanations help illustrate human activity in the area from approximately 40,000 to 15,000 years ago, providing a clearer picture of the prehistoric environment and archaeological discoveries.
There are now archaeological sites in Japan that are larger or contain more artifacts than Iwajuku. The importance of Iwajuku, however, lies not in its physical size but in its historical significance as the site that opened the door to research into Japan’s earliest known human history.
The discovery of a single archaeological site pushed the known beginnings of human history in Japan back by tens of thousands of years.
Iwajuku Ruins therefore remain a symbolic site in the study of human history in the Japanese Archipelago and an indispensable part of the history of Japanese archaeology.
Located across the Shikada-yama Hills southeast of Mount Akagi, Iwajuku Ruins offer visitors an opportunity to experience the deep history of Japan in a peaceful natural setting.
Walking through the quiet hills while imagining how people lived here approximately 30,000 years ago provides a unique way to connect with Japan’s distant past.
A visit to Iwajuku Ruins and Iwajuku Museum is a journey back to one of the earliest chapters of human history in the Japanese Archipelago. When exploring Midori City, it is well worth taking the time to discover the archaeological story behind this remarkable site.