The Onaka Ruins are an important archaeological site in Harima Town, Kako District, Hyogo Prefecture. Dating from the final phase of the Yayoi period, approximately 1,900 years ago, to the beginning of the Kofun period, the settlement provides valuable insights into life in ancient Japan around the time of Queen Himiko, the legendary ruler associated with the kingdom of Yamatai. Several pit dwellings have been reconstructed, allowing visitors to imagine what the settlement once looked like. On June 22, 1967, the site was designated a National Historic Site of Japan.
The Onaka Ruins were discovered on June 24, 1962, by three students from Harima Junior High School. After hearing local residents recount how numerous octopus-fishing pots had been unearthed during construction of the former Beppu Railway Tsuchiyama Line in the Taisho period, the students investigated an area where soil had previously been excavated south of Yamanoue Sumiyoshi Shrine, north of the present archaeological site. There, they found a large quantity of pottery fragments.
The recovered artifacts were initially stored at Zenpukuji Temple, approximately 700 meters to the southwest. Following the submission of an official discovery report to the town and prefectural boards of education, specialists from Hyogo Prefecture began investigating the site.
From December 1962 to November 2003, a total of 20 archaeological investigations were conducted at the Onaka Ruins. The excavations were led primarily by the Harima Town Board of Education and the Hyogo Prefectural Board of Education. Researchers examined the settlement’s extent, archaeological features, and surrounding environment, while also carrying out investigations connected with the site’s preservation and development as a public attraction.
The 18th through 20th excavations were particularly important because they helped establish the historical significance and contents of the site in connection with plans for the Hyogo Prefectural Museum of Archaeology.
Harima Town is the smallest municipality in Hyogo Prefecture by land area, and approximately 30 percent of its territory consists of artificial islands created through land reclamation. The town is located about 40 kilometers from Kobe and 25 kilometers from Himeji. The Onaka Ruins lie in the Onaka 1-chome area, between National Route 2 to the north and National Route 250 to the south.
The region has a Seto Inland Sea climate, characterized by relatively mild temperatures and limited rainfall throughout the year. Its location near transport routes and its surrounding natural resources help explain the appeal of this area for settlement in ancient times.
The archaeological site covers approximately 70,000 square meters and occupies the edge of a Pleistocene terrace. It stands at an elevation of about 14.5 meters and lies near several bodies of water, including Tsumeike Pond and Kitsunegai Pond, as well as the Kise River. The area is situated near the eastern edge of the floodplain associated with the Kakogawa River.
The terrain slopes gently from east to west. This landscape, together with the nearby waterways, provides useful context for understanding the environment in which the ancient settlement developed.
Numerous remains of pit dwellings have been found at the Onaka Ruins. These structures vary in shape, including circular, square, and hexagonal floor plans. Pit dwellings were common forms of housing in prehistoric Japan, with living spaces constructed partly below ground level. Several examples have been reconstructed at the site so that visitors can better understand the appearance and construction of ancient homes.
The reconstructed buildings use reeds sourced from Okayama Prefecture’s Bizen area. Craftspeople from Miyama, Kyoto, took part in recreating the traditional structures, helping preserve construction techniques associated with Japan’s ancient past.
Many objects used by the settlement’s inhabitants have been unearthed and are displayed at the Harima Town Local History Museum. These include Yayoi-period pottery such as dishes, pedestal bowls, and jars, as well as Haji pottery, stone arrowheads, fragments of a mirror decorated with an inward-facing floral design, fishing-net sinkers, and clay imitations of mirrors.
Together, these artifacts offer clues about food preparation, fishing, craftwork, and the cultural practices of the people who lived here nearly two millennia ago.
The Onaka Ruins were discovered on June 24, 1962, when the first archaeological investigation began. They received designation as a National Historic Site on June 22, 1967. On September 28, 1974, the prefectural historic park known as Harima Onaka Ancient Village opened to the public. The Harima Town Local History Museum followed in November 1985.
The annual Onaka Ruins Festival began on August 3, 1990. On October 13, 2007, the Hyogo Prefectural Museum of Archaeology opened next to the historic site. In 2012, the community marked the 50th anniversary of the ruins’ discovery.
Every autumn, the Onaka Ruins Festival brings the ancient settlement to life through activities inspired by Yayoi-period culture. The event is popular with local residents and visitors, offering an engaging way to explore the area’s archaeological heritage and learn about life in prehistoric Japan.
The ruins have been developed as the prefectural historic park Harima Onaka Ancient Village. The reconstructed dwellings and neighboring museums form a wider cultural destination where visitors can explore the transition from the Yayoi period to the Kofun period.
The Harima Town Local History Museum introduces the history and culture of the local area. In addition to artifacts excavated from the Onaka Ruins, its exhibits cover notable figures from Harima, the region’s railway history, and other aspects of community life.
Highlights include materials related to Joseph Heco, known as a pioneer of Japanese-language newspapers, and Denbei Imazato, who was involved in the development of the Arai canal. The museum also introduces the history of the former Beppu Railway. Outdoors, visitors can see a locomotive and passenger carriage from the railway, with an opportunity to experience boarding the historic rolling stock.
Opened on October 13, 2007, the Hyogo Prefectural Museum of Archaeology conducts archaeological research, presents discoveries from across the prefecture, and offers hands-on educational programs. The museum also has a department dedicated to excavating and investigating buried cultural properties, supporting research and the training of people working in archaeology.
Designed to harmonize with the historic landscape, the building has a relatively low profile and incorporates greenery on its walls and rooftop. Visitors can view the Onaka Ruins through glass from inside the museum and from its rooftop garden. A café operated by Kobe Fugetsudo is located in the entrance lobby.
The museum’s collections and displays include a full-scale reconstruction of an ancient boat, a reconstructed stone coffin associated with the front chamber of Mise-Maruyama Kofun, human skeletal remains known as the Akashi human bones, and a reconstruction of the stone burial chamber from Kumabe Kurumazuka Kofun. Actual human remains excavated from sites across Hyogo Prefecture, dating from the Jomon through the Kofun periods, are also represented in the collections.
The museum holds a wide range of important archaeological materials excavated throughout the prefecture, including objects designated as Hyogo Prefecture Important Tangible Cultural Properties. Its exhibition spaces include the Time Gallery, which arranges excavated pottery chronologically; an introductory exhibition room; the hands-on Excavation Plaza; themed galleries; and special exhibition rooms. Visitors may also have opportunities to observe archaeological work and the conservation treatment of metal artifacts.
Additional facilities support practical learning, research, and preservation. These include hands-on learning rooms, a lecture hall, an archaeology information area, a multipurpose hall with 180 seats, artifact-processing rooms, and storage facilities for archaeological objects, photographs, and drawings.
The Onaka Ruins and their neighboring museums offer an accessible introduction to the ancient history of Japan. The reconstructed pit dwellings help visitors picture everyday life in a Yayoi-period settlement, while the museums provide a closer look at the objects, research, and archaeological techniques that bring the past into focus. With educational activities suitable for families and visitors of different ages, the site is an excellent destination for anyone interested in archaeology, ancient culture, or the history of Hyogo Prefecture.
From Tsuchiyama Station on the JR Kobe Line, also known as the Sanyo Main Line, the ruins are approximately a 12-minute walk. From Harimacho Station on the Sanyo Electric Railway, the walk takes about 25 minutes. By car, the site is approximately 3 kilometers from the Akashi-Nishi Interchange. Paid parking is available in the surrounding area.