The Remarkable Discovery by Tadahiro Aizawa
Stone Tools Found in the Kanto Loam Layer
Around 1946, Tadahiro Aizawa, an independent researcher of archaeology, discovered chipped stone tools in a layer of reddish soil known as the Kanto Loam.
At the time, archaeologists generally regarded the Kanto Loam as the natural ground layer and rarely investigated below it. The Jomon period was then considered the oldest known cultural period in Japan, so there was little reason to search for evidence of an even earlier human presence.
Aizawa, however, continued investigating the evidence he had discovered. In 1949, he conducted an archaeological excavation together with a research team from Meiji University.
The excavation uncovered clearly worked stone tools from within the Kanto Loam layer. This provided archaeological evidence that a Paleolithic culture had existed in Japan.
Two Distinct Stone Tool Culture Layers
Iwajuku I Culture
Excavations at the site revealed two distinct stone-tool cultural layers at different depths.
The lower layer, known as the Iwajuku I Culture, is estimated to date to approximately 30,000 years ago. Stone tools found here include chipped stone axes and scraping tools made from shale.
Charred material was also discovered, suggesting that the people living here may have made use of plant resources and engaged in activities involving fire.
Iwajuku II Culture
The upper layer, known as the Iwajuku II Culture, dates to approximately 20,000 years ago.
Researchers discovered knife-shaped stone tools made from a variety of materials, including obsidian and agate. These finds provide evidence of changes and developments in stone-tool technology over time.
The existence of two cultural layers makes Iwajuku more than a site representing a single moment in history. It provides important evidence for understanding changes in human culture and technology over a long period.
The Concept of the “Iwajuku Period”
The period represented by the Iwajuku Ruins is generally described as the Paleolithic period, or sometimes the Pre-Pottery period. However, the Iwajuku Museum uses the term “Iwajuku Period” to emphasize the distinctive cultural characteristics of Japan’s earliest prehistoric era.
This was a time when people lived without pottery and relied largely on hunting and gathering. The term is intended to highlight the distinctive archaeological history of the Japanese Archipelago during this early period.
Following the Iwajuku discovery, archaeological sites dating to the same broad period were identified throughout Japan. Today, more than 10,000 Paleolithic sites have been confirmed across the country, and Iwajuku is regarded as the discovery that helped open the way to this field of research.
Iwajuku Museum and Iwajuku Dome
Iwajuku Museum
Iwajuku Museum, located beside the archaeological site, introduces the stone tools discovered here, the history of the excavations, and the natural environment in which prehistoric people lived.
One of the museum’s highlights is a full-size replica of a mammoth skeleton, which helps visitors imagine the environment of the Ice Age.
The museum also displays an antlered deer skull and exhibits explaining how Paleolithic stone tools were produced. These displays make the site accessible and engaging for visitors of all ages, including families with children.
Iwajuku Dome
At Site B of the Iwajuku Ruins stands the Iwajuku Dome, officially known as the Historic Site Iwajuku Ruins Remains Preservation and Observation Facility.
Inside the dome, visitors can observe an actual cross-section of the Kanto Loam geological layers in which Paleolithic stone tools were discovered.
Video presentations and other interpretive materials help visitors understand human activities in the Japanese Archipelago from approximately 40,000 to 15,000 years ago, providing a more complete picture of life during the prehistoric period.
Why the Iwajuku Ruins Are So Important
There are now archaeological sites in Japan that are larger than Iwajuku or contain a greater quantity of artifacts. The importance of the Iwajuku Ruins, however, lies not in their size but in their historical significance as the site that opened the door to research into Japan’s earliest known human history.
The discovery at a single archaeological site pushed the starting point of Japanese human history back by tens of thousands of years.
Iwajuku therefore remains a symbolic site in the study of human history in the Japanese Archipelago and an essential chapter in the development of Japanese archaeology.
A Journey into Japan’s Deep Prehistory
The Iwajuku Ruins extend across the Shikada-yama Hills southeast of Mount Akagi. Surrounded by a natural landscape, the site provides a peaceful setting in which to think about the people who lived here approximately 30,000 years ago.
Walking through the quiet hilly landscape while imagining the lives of prehistoric people offers a different kind of sightseeing experience—one that connects visitors with a period long before written history.
When visiting Midori City, consider combining the Iwajuku Ruins with Iwajuku Museum and Iwajuku Dome. Together, these sites offer an opportunity to travel back to the earliest known chapters of human history in the Japanese Archipelago and discover how one remarkable archaeological discovery changed our understanding of Japan’s past.