Ireibaru () is a major archaeological site of Okinawa Island, located in town of Chatan on the western coast. It includes occupations for the whole duration of the Kaizuka period, for the Gusuku and Early Kingdom periods, the early modern period and the modern period. It is the only site in Okinawa Prefecture to show occupations for each of the phases of the Kaizuka period. It yielded large quantities of artefacts in perishable materials conserved in wet context. It has been designated as a National Historic Site in 2010. Chatan Museum opened on 20 November 2024 at the location of the site.
Location Address: Okinawa, Chatan, Ihei1-1 (formerly Ihei, Ireibaru 144 and 163).
Coordinates:
Ireibaru is located in Chatan, a town on the western coast of Okinawa Island. Before the war, this area corresponded to the eastern side of the settlement of Irei, that was destroyed to build Camp Kuwae. It is an alluvial area at the foot of low hills, enclosed by higher plateaus and a river. The plateaus on the back are about 30 m high. A spring named Ūchi-nu-kā is located at the foot of the hill and formed wetlands and a stream that watered the small alluvial plain before it poured into the Nagasa-gā River by its estuary on the western side of the archaeological site.
Discovery and excavations The area where Ireibaru is located is rich in archaeological sites. In 1988, during construction works along the river, ceramic sherds and bones were disclosed, leading to the intervention of archaeologists from Chatan Town Board of Education. The archaeologists identified the area on the sand dune as an archaeological site and named it Ireibaru A. Since the construction works would not damage it furthermore, it was not immediately excavated. The same year, at the occasion of construction works on a water drainage facility in Camp Kuwae, another site named Ireibaru B was discovered and partly excavated.
In 1996, it was decided by the Special Action Committee on Okinawa that the northern part of Camp Kuwae should be returned to Chatan in March 2003. In the scope of this retrocession, the Japanese Agency for Cultural Affairs and Okinawa Prefecture Board of Education started in 1995 a three-year survey of the buried cultural properties in the concerned 40.5 ha area. It resulted in the disclosure of ten archaeological sites and six artefact scatters. The archaeological sites included the previously mentioned Ireibaru A and B, as well as Ireibaru C in the wetland, and Ireibaru D and E.
After the archaeological testing in 1996, excavation surveys were implemented between 1998 and 2005. Ireibaru C was excavated between 1998 and 2002, Ireibaru A between 2002 and 2005. The excavations made it clear that Ireibaru A and Ireibaru C were in fact the same site, and since it appeared to be of utter importance for the Kaizuka period studies, the two sites were merged under the name "Ireibaru Site" in 2006, while Ireibaru B, D and E remained independent entities. Only Ireibaru is registered as a National Historic Site.
Site description The site measures 15,000 m2 and includes a wetland part watered by Ūchi-nu-kā (formerly Ireibaru C) and a sand dune part on the west (formerly Ireibaru A). People lived on the sand dune (settlement remains) but conducted most of their daily activities (food processing) by the stream and the wetland. The site comprises occupations of the Kaizuka period from the Early Kaizuka Period Phase I to the Late Kaizuka Period, of the Gusuku and Early Kingdom period and the remains of the pre-war settlement.
The part of the wetland area by the foot of the hill includes occupations of the Early Kaizuka Period Phase I, Phase II, Phase III and Phase IV. The sand dune was formed later in the chronology and shows occupations as soon as it starts being formed in the Early Kaizuka Period Phase III. It is then continuously occupied with remains of the Early Kaizuka Period Phases IV and V and Late Kaizuka Period Phase I. During this long period, the sand dune was damaged twice possibly by tidal waves or very strong storms. The first time was during the Early Kaizuka Period Phase IV when a part of the settlement disappeared in the collapse of the dune, and the second time during the Late Kaizuka Period Phase I. After the second collapse of the sand dune, it reconstructed slowly, and the next occupation of the area is dated of the 13th century during the Gusuku Period, when a new settlement was built there.
The site yielded a large quantity of pottery, and especially Sobata pottery of the Early Jōmon Culture of Kyūshū Island, but also lithics, wild boar bones, land turtle bones, fish bones and marine shells. It is particularly famous for the conservation in wet context of perishable material such as seeds, fruits and wood.
Site chronology Early Kaizuka Period Phase I (4800-4000 BCE) The first attested human occupation was found for the Early Kaizuka Period Phase I, when people lived in the area around the spring. Artefacts (Nantō-tsmegatamon pottery and stone tools) were found, but no remain of dwellings could be identified. It is highly probable they used the rock shelters of the nearby limestone hill. This is a period when the sea level was higher than nowadays, and the site was located on the shore.
Early Kaizuka Period Phase II (3500-3000 BCE) This is the period of occupation for which the use of the area near the water seems the most intense. Peebles between 5 and 40 cm large deposited on the southwestern side of the site and it is from this pebble layer that the imported Sobata pottery from the Early Jomon culture of Kyūshū Island was found. The layers from this period also yielded stone tools, wooden implements, shells, animal and fish bones, seeds, acorns and nuts. Bamboo baskets were installed on the southeastern side of the site, in the marsh, where the pebbles were scarce, to wash the tannin from the acorns and conserve them underwater. It is thought the dwelling site was located on the sandy area that had formed on the western side of the hill. The sea level was quite similar to the one in the preceding period and the site was still on the shore. The coral reefs started to form.
The shift toward marine resources, a well-known event in Okinawan prehistory linked to the development of the coral reefs, is observed in Ireibaru as soon as the Early Kaizuka Period Phase II, which is early compared to the general tendency in Okinawa Island, where the move can be seen rather in Phase III. This can be explained by the favourable marine environment by the site, with a protected bay that sheltered numbers of fishes even before the full development of the coral reefs.
Early Kaizuka Period Phase III (by 2500 BCE) The wetland occupation for this period was found above the pebbles layer that had filled the southwestern part of the site. It yielded wood fragments cut into planks, stone tools Omonawa-zentei pottery (types III to V), Nakadomari pottery (types A and B) and a wooden container.
Around the foot of the hill by the southwestern and southern side of the wetland, a sand dune started to form, from which three hearths, a concentration of marine shells in a large pit that might have been originally a pit-dwelling, and several postholes were disclosed, showing that the settlement extended westwards. Two fragmentary human bones (a femur and a tibia) were retrieved from the Early Kaizuka Period Phase III contexts. They were isolated but might hint at the presence of a funerary area in the vicinity. The dune also yielded Omonawa-zentei pottery and Nakadomari pottery. Sea and land mammal bones and artefacts made from them, as well as pottery and lithics, have been found in this residential area. The sea level started to decrease and the shore got further. The coral reefs were better developed than during the preceding period.
Early Kaizuka Period Phase IV (by 1500 BCE) During this occupation, the population do not use the wetland as much, but the remains are more numerous on the sand dune. The sand dune is spreading slowly westward and two pit-dwellings were found extending southeastward, accompanied by four stone concentration areas and eight earth pits. The dwellings are squared with rounded angles, about 3x3 m large, paved with flat stones. The stone concentrations might be dwellings as well, but they do not show any voluntary excavation of the ground to create a pit-dwelling.
The settlement yielded stone tools such as saddle querns, Omonawa-tōdō pottery, Katoku pottery, Ichiki pottery, Iha-Ogidō pottery and animal and fish bones. It is during this period that the sand dune is damaged for the first time, by a tidal wave or a strong storm, destroying part of the dwellings.
Early Kaizuka Period Phase V (by 500 BCE) The use of the wetland seems to decline furthermore, but a wooden comb was found in one of the former water channels of the area. A new sand dune is developing and a settlement is again installed at this location, extending further northward. A hearth lined with stone and an earth pit were disclosed, but no dwelling could be identified. The discovery of isolated human bones (a skull) hints at the presence of a funerary area in the close vicinity. In addition to the wooden comb, the artefacts include local Kayauchibanta pottery, Uzahama pottery, Nakabaru pottery, obsidian imported from Kyūshū and jade from Itoigawa on Honshū Island, showing that the extent of the trade sphere increases.
Late Kaizuka Period Phase I (by the beginning of the Common Era) The use of the wetland is still low, but the use of the sand dunes increases with the development of the dwelling area from which many postholes were disclosed. It was however not possible to attribute the postholes to precise dwellings. The site yielded sherds of a large jar from the Early Yayoi culture, a flat edge stone axe and conch shells bracelets of the Morioka type, trade goods that had until then never been found in Okinawa, despite the fact they were produced there and exported to Kyūshū Island. It is at this period that the dune is damaged again by a tidal wave or a strong storm, in which the settlement is partly destroyed.
Gusuku and Early Kingdom periods (1200-1500 CE) A mangrove forest developed in the wetland before the beginning of the Gusuku period (directly dated of 1140 ±60 CE). It was followed chronologically by thick deposits (1 m) that included a lot of fresh water snails and were interpreted as earth from fields and paddy fields, extending from the Gusuku period to WWII. It was the first time on Okinawa that remains of antique paddy fields were the object of an archaeological survey. During the Gusuku period, a new sand dune got formed, on which a new settlement was built. It extended this time northwestward and is considered as the foundation of the Irei settlement that perdured until the war. The Gusuku period settlement was characterised by the discovery of a large number of postholes from the houses and the granaries. It was however not possible to attribute the postholes to precise dwellings. The wooden posts were conserved in two of the postholes. The Gusuku and Early Kingdom periods can be divided into three stages with imported talc pots, kamuiyaki ware and Chinese white porcelain for Stage I (11-13th c.), celadon for Stage II (13-15th c.) and blue-and-white porcelain, celadon and sancai porcelain for Stage III (15-16th c.), showing a slow shift in the maritime trade routes. Those imported artefacts are accompanied by locally produced Gusuku pottery. Most of the Chinese porcelain associated with the postholes area is dated of the 15th to 16th century. The older artefacts were retrieved from a part of the site with no archaeological structures.
Early Modern and Modern periods (17th c.-1940)