Koriyama Ruins (郡山遺跡)

The Koriyama Ruins are the site of an ancient kanga (public office) located in the present Koriyama, Taihaku Ward, Sendai City, Miyagi Prefecture. From the middle of the seventh century to the early eighth century (possibly 724) the older stage I kanga, the following stage II kanga and Koriyama-haiji Temple at the second stage were operated. It is presumed to have been the Kokufu (state office) of Mutsu Province. National historic site.

Location and Pre-stage I Settlements

The Koriyama Ruins are now located in 2 to 6-chome, Koriyama, Taihaku Ward, Sendai City, Miyagi Prefecture, once belonging to Natori County, Mutsu Province. It is on the natural embankment between two rivers, near where the Natori-gawa River running through the southern part of Sendai City and the Hirose-gawa River (Miyagi Prefecture) join. There are a lot of ruins about the area and the sites where relics of the past are buried lie side-by-side and link together. The Koriyama Ruins are one portion of the district.

The Tomizawa Ruins in the west of the Koriyama Ruins are the ruins of sectional rice fields and settlements. Some Yayoi pottery has also been found in the Koriyama Ruins. From bottom up came potteries of Aokibatake-style (青木畑式土器) in the early Yayoi period, Sakiyama-style in the middle of the Middle Yayoi period and Masugata-style in the end of the Middle Yayoi period. Remains of rice fields before the middle of the middle Yayoi period were also found.

Stage I Kanga
It is assumed that the office was 620m long from south to north, 400m long from east to west, the base line of the building pointed 50 to 60 degrees west from true north, and the front was at the southeast side. The surrounding structure was a wall built of lumber put up in a row, the entire shape formed a rectangle with the longest side 560m long and the short side 295.4m long. Of the four sides the northeast side has not been found, so the exact length of the long side remains unknown.

The inside was partitioned by boarding fences and a row of lumber, and a lot multiple buildings were built in the compartment. We know that the central compartment may have been the government office, and around it there were a warehouse compartment, the north multipurpose house compartment, the south multipurpose house compartment and the pit house compartment, but still we know only part of the whole thing. There was a blacksmiths' workshop in the south of the north multipurpose building compartment.

Most of the unearthed potteries were local ones, but some were Kanto-style Haji potteries and a small number of Kinai-style Haji potteries called Asuka type III were also found.

The age can be thought to be from the middle seventh century to the late seventh century. The building placement and the existence of a group of warehouses were, under the ritsuryo system (a system of centralized government based on the ritsuryo code), similar to those of the gunka (regional office), but not of the kokuga (state office), but there were inner compartments which the gunka did not have.

It is pointed out that the South Koizumi Ruins, a large settlement in the Kofun period, scaled back because of the construction of the stage I kanga. In the latter half of the seventh century it was an important place for the Yamato Dynasty to rule Mutsu Province, and speaking a little more daringly, it was presumably the early provincial capital of Mutsu Province.

Stage II Kanga
The stage II kanga was established, on the standard of true north, where the destroyed stage I buildings were. The positions of the four sides are known. The surrounding structure is 422m long from south to north, 428m from east to west and consists of a lumber wall and a big ditch. The moat was made of pillars 25 to 30cm in thickness that were closely put up in a row, and the ditch around it is 2.5m in width and 60cm in depth. The ditch went round the outside, 9m away from the lumber row.

At the center of the south side there were a remainder of the gate and tower-like building at the southwest and west corners. No other gate except the south gate has been found. A little to the south of the center there is a structure supported by posts in the ground extending long from east to west and with eaves on the four sides, which is assumed to have been the main building of the government office. To its north there is a stone paved place and a stonework pond to the northeast. In the north and west, as was expected, there was a stonework ditch which let water run into the pond.

There were also buildings outside of the south of the surrounding structure. In the southwest an attached temple (Koriyama-haiji Temple) was built around the same time. Here roof tiles similar to those of Taga-jo Castle were excavated.

Unearthed potteries are older than those of early-stage Taga-jo Castle, the kokufu (state government) of Mutsu Province after the eighth century. Because the basic arrangement is the same as that of other kokufu under the ritsuryo system, it is assumed to have been a kokufu prior to Taga-jo Castle. However, stonework ponds are not seen in other kokufu except for in Asuka. Some theories suggest that it was related to the ritual of obedience of Ezo.

The stage II kanga is thought to have existed from the late seventh to the early eighth centuries and was abolished before and after the foundation of Taga-jo Castle. According to the epigraph of Taga-jo Castle monument when Taga-jo Castle was built in 724, it was abolished in this same year. Koriyama-haiji Temple existed until the latter half of the eighth century.

History of Excavation and Current State

Though roof tiles similar to those of Taga-jo Castle were found in the Koriyama Ruins at the place that was later called Koriyama-haiji Temple, research had been untouched for a long time. In 1979 Sendai City Board of Education began investigating and confirmed the existence of the abandoned temple and stage I and II kanga. Since then tens of excavations were performed, and in 2006 to date they have been going on.

In the early stage of excavation there was a presumption that it was a gunga (regional public office) of Natori County along with a kokufu of Mutsu Province or a stockade of a castle whose name does not appear in documents, but at present the accepted theory is that the stage II kanga was the kokufu of Mutsu Province before Taga-jo Castle was. In 1987 Yayoi pottery was found in the lower layer under the kanga ruins, suggesting that there was a settlement prior to the kanga.

The remains are located in the ground about three to five meters deep. They had hardly been damaged because this area was a paddy field zone before. Because they are now under the ground of an urban area, research can be conducted only in a small compartment when there is construction work. High buildings are not permitted in the Koriyama Ruins Zone.

Now part of the zone is included in the area of "Asuto-nagamachi," the Nagamachi subcenter, and a land readjustment project and excavation accompanied by the project have been going on. In the adjoining ruins "Nishidaihata Ruins" (locally often called "Nishidaibatake") and Nagamchi East Station Ruins, the remains of residences and so on where people working in the Koriyam Ruins had presumably lived were found and excavated, but they had been damaged probably by the construction of old Japanese National Railway (JR) Nagamachi Rail Center and old JR Nagamachi Yard (now both of them are abolished) and work of burying infrastructure.

Moreover, in Sendai City Koriyama Junior High School which is in the Koriyama Ruins zone there is a data room which reproduces the remains on the first floor (which is 1.5m higher than the ground level, but the room is usually closed with no visitors allowed.

On July 28, 2006, about 4.3 square kilometers of the important part of the ruins (now most of the part is fallow fields or idle land) was designated as a national historical site named "Sendai Koriyama Kanga Ruins Group."