Monograph No. 70
Report of Nara Palace Site Archaeological Investigations XVI: Investigations at the Ministry of Military Affairs Area
Summary
This volume reports on the excavation results at the district alleged to be Ministry of Military Affairs (Hyoubusho 兵部省) in the Heijo 平城 (Nara 奈良) Palace Site which is designated as a special historical site.
A southern part of State Halls Compound (Choudouin 朝堂院) at the Eastern block of the Heijo Palace Site had been investigated through seven excavation projects in the 1980s and the 1990s. The investigated area covers approximately 200 meters from east to west, 100 meters from north to south. The volume is an outcome of the investigations by National Research Institute for Cultural Properties, Nara.
The excavations confirmed two layers of archaeological structure clusters; 1) a group of structures constructed at the establishment of the Heijo Palace Site (the lower layer), 2) and another group constructed after the former buildings had been abandoned (the upper layer). At the close southeast of the investigated area, Mibu-mon Gate, the eastern one of the three gates on the southern edge of the palace, had been opened on the south of Great Palace Compound Wall. Nevertheless, at the time of the lower layer, the tamped earthen wall for the Great Palace Compound Wall had not yet been constructed. Instead, there had been an embedded pillar wall in a large scale from east to west, at 16 meters north of the later Great Palace Compound Wall, in order to mark off the facilities in the southern part of the palace. We have not uncovered any distinct archaeological features from the lower layer. It is partly because the archaeological structures on the upper layer were very well preserved, hi order to uncover the structures of the lower layer extensively, the well-preserved upper layer structures need to be removed, and thus, destroyed, which does not seem to be an appropriate handling of the special historical site. We were expected to investigate the archaeological structures of the lower layer with the possible least destruction of the upper layer. Notwithstanding, we judged that there were not many structural remaining of the buildings on the lower layer as a result of the partial, but careful excavations.
On the upper layer, the investigation uncovered a square compound approximately 73 meters (250slmku 尺) on a side. Inside the compound, eight buildings roofed with tiles and constructed on stone bases were and arranged in 
shape on the whole. At the center of the compound, the main building stretching from east to west stood. At the north of this, three buildings stretching from east to west were lined up side by side. At each side of the main building, the two buildings stretching from north to south were allocated respectively. We found the plan within the compound is typically symmetrical. This is the first example of shape plan within the Heijo Place Site, apart from the palace area directly related to the emperor, such as Imperial Residence and State Halls Compound. In fact, this type of plan had also widely been adopted by the central parts of the local government offices, which has significant implications to consider developments in the governing of remote local regions.
Moreover, a clear hierarchy of buildings within the compound was revealed by the analysis of the architectural style and the heights of the foundation platforms. The observation would greatly contribute to define the function of each building, as well as to examine the character of the archaeological structures uncovered in the other sections.
A cluster of archaeological structures on the upper layer was judged to be the traces of Ministry of Military Affairs, grounded on the several results from the excavations. Ministry of Military Affairs in the Nara Period dealt with the personnel affairs of military officers, management of army, weapons, and military facilities. The ministry took the great responsibility for networking of military information and installations all over Japan. It originated from Heiseikan, which first appeared in the historic document in 675AD, and was renamed to Hyobusho by the administrative codes in 701AD (Taihouryou 大宝律令).
The past investigations revealed that Ministry of Personnel Affairs (Shikibusho 式部省) had been located in the symmetrical position to Ministry of Military Affairs reported in this volume, with the centre of Mibumon Gate as an axis. The building arrangement and scale were almost the same regarding these two compounds. Ministry of Personnel Affairs seized real power in politics, dealing with the personnel affairs, but its facilities were almost identical to Ministry of Military Affairs based on the analysis of excavated archaeological structures, which was followed by the Heian Palace established in the later period. Historical document showed that Ministry of Military Affairs, which had not originally held as much power as Ministry of Personnel Affairs, increased its power in the early 730s.
Archaeological structures of Ministry of Military Affairs revealed by the investigations in this volume belonged to the upper layer, and thus we have not yet confirmed the ministry in the earlier stage. Hence, we consider the construction of Ministry of Military Affairs on the upper layer had been closely related to the political movement of increasing its power as much as Ministry of Personnel Affairs, in the early 730s.
There are some questions to be further investigated. For instance, there is a contradiction regarding the establishment date of the ministry when the excavated roof-tiles were taken into consideration. Most roof-tiles used for the buildings in Ministry of Military Affairs were sets of round eave tiles in6282 G style and flat eave tiles in 672IF style, or sets of 6225A style (round) and 6663Cb style (flat). It has been generally accepted that those eave-tiles were used at the time of the large scale construction on State Halls Compound in the Eastern block, the second Great Audience Hall (Daigokuden 大極殿), and other central parts of the Heijo Palace just after 745AD, which contradicts the establishment date of Ministry of Military Affairs. Nevertheless, some researchers recently pointed out that those roof-tiles could be dated back to earlier than 740AD, although it has not yet been secured.
The answer of this problem cannot be finalized in this volume. It needs further investigations of surrounding office areas, especially Ministry of Personnel Affairs and Council of Religious Affairs (Jingikan 神祇官) in the east of Ministry of Military Affairs. Moreover, more detailed analysis of the typology of eave-tiles would lead to the clearer historical facts.
In the investigations in this volume, large amount of pottery and wooden tablets uncovered in the main drainage ditch SD3715 flowing southwards around the western edge of the investigated area. Excavated pottery, especially Sue-ware, had distinct character of the end of Nara Period. The contents of 176 excavated wooden tablets also report on the surrounding environment of the ministry to us. In addition, several pit-hole dwellings dated to the Yayoi Period were discovered around the northern edge of the investigated area. Those dwellings were dated to the end of the Early Yayoi Period, which is very rare in the northern part of Nara Basin. Many stone reaping knives, stone arrowheads, stone axes and adzes of the Yayoi Period were also excavated, and a cluster of the Early Kofun Period Haji-ware were excavated from the well, which would help to reconstruct history of this area before inauguration of the Heijo Palace.
Furthermore, based on the revealed facts of a typical office compound, Ministry of Military Affairs, this volume attempts to reconsider the plots of office compounds within the Heijo Palace reported in the preceding investigations. Particularly, the establishment dates for the respective office compounds were focused, in relation to the standard measurement adopted in each plot.
We also carefully examined archaeological structures of the roads among the palace and office compounds within the Heijo Palace. Besides, we argue against recently accepted theory on the consideration of remaining land plot within the Heijo Palace Site. It is generally accepted now that the remaining land plot is the result of farm management after the Heijo Place was abandoned. Nevertheless, the land within the Heijo Palace Site was mostly plotted by the ridges between rice fields, which reflected on the sectioning of official compounds when the Heijo Palace had been abandoned. This volume also attempts to reconstruct the land plot of the whole Heijo Palace Site, which had been uncompleted so far.
2005年3月30日 発行
平城宮発掘調査報告XVI
奈良文化財研究所学報第70冊
兵部省地区の調査
本文編
