Monograph No. 79
STUDY ON THE RECONSTRUCTION OF THE FIRST IMPERIAL AUDIENCE HALL, HEIJO PALACE 1 Platform/Foundation Stones（2009）
Research Report Vol. 79
Nara National Research Institute for Cultural Properties
English Contents and Summary
Contents
Chapter 0 Process of reconstruction and publication of report
1 Process of restoration 1
2 Process of restoration review 5
3 Publication of report 13
Chapter I Process of review and creation of report
1 Process of review 15
2 Creation of report 17
Chapter II Excavated structural remains 19
Chapter III Case study
1 Study of the foundation stones of the First Imperial Audience Hall, Heijo Palace
A Introduction 27
B Importance of perspective based on stone materials 27
C Transition of foundation stones 28
D Data of the foundation stones used within the Heijo Palace 30
E Foundation stones of the First Imperial Audience hall 34
2 Platform and foundation stones of the Kuni Palace
A Introduction 37
B Excavation survey results 37
C Architectural explanation of excavation results 39
D Study on existing foundation stones 39
3 Form and exterior stone materials of the platform faced with hewn stones
A Introduction 42
B Form of platform faced with hewn stones 43
C Size of each exterior stone material of platform faced with hewn stones 45
D Conclusion 50
4 Case examples and forms of platforms
A Case examples of structural remains of stairs 51
B Specifications of stairs seen in ancient architecture 61
C Stairs seen in structural methods 65
5 Case examples and forms of double platforms
A Main hall of Horyuji Temple and Asukadera Temple 67
B Actual examples of double platforms 68
C Cases on the Korean Peninsula 75
D Functions of double platforms and the first imperial audience hall of Heijo Palace 78
6 Pavement of platform
A Existing structural remains 82
B Case examples of excavations 83
C Pavement of platform surface in ancient times 90
7 Platform of Hanyuan Hall (Darning Palace, Chang’an Castle, Tang dynasty) and the 37th hall ruins of Renshou Palace (Sui Dynasty) and Jio Cheng Palace (Tang dynasty)
A Hanyuan Hall of Darning Palace, Chang’an Castle, Tang dynasty 92
B Renshou Palace (Sui dynasty) and Jio Cheng Palace (Tang dynasty) 94
C Comparison with Japanese case examples 95
Chapter IV Process of reconstruction
1 Review of platform plane
A Restoration of the platform based on the 295th survey results 96
B Error of measured values and review of platform plane 103
2 Height and form of platform
A Review of the height and form of the platform 109
B Specifications of platform 112
C Specifications of stairs 114
3 Pavement of platform 116
4 Foundation stones 117
Chapter V Reconstruction plan 118
Contents/summary of the English version
Summary
In 710, the Nara capital (Heijyo-kyo 平城京) was constructed in the area currently known as Nara City. The Heijo Palace was located at the center of the northern area of the capital, extending approx. 1.3 kilometers in the east-west direction and one kilometer in the north-south direction. The Heijo Palace included not only the imperial residence, but also spaces for rituals and the affairs of State. During the first phase of construction of the Heijo Palace, the first imperial audience hall compound (Daiichiji-Daigokudenin 第一次大極殿院) was built in the center. The first imperial audience hall (Daiichiji-Daigokuden 第一次大極殿院) was the main building of the first imperial audience hall compound. The national Capital, however, was relocated to the Kuni Capital in 740. At that time, the first imperial audience hall was also moved to the Kuni Palace, and, in later years, reused as the main hall of the Yamashiro-kokubunji Temple (lit. the Buddhist temple of Yamashiro district). However, the first imperial audience hall was dismantled in the intervening years. Although the national capital was relocated again to Nara capital in 745, the site on which the first imperial audience hall was originally built had already been occupied by a new palace; while the platform of the first imperial audience hall had been largely removed. In 784, the capital was relocated thrice to the Nagaoka Capital place, and the historic role of Heijo Palace terminated. Since then, in the early 9th century, another palace was transiently built at this site, but it continued for only about 15 years before being abandoned. The Heijo Palace site has, as a result, reverted to agricultural land use.
In 1922, the Heijo Palace site was designated as a national historic site. Since 1952, subsequently, the Nara National Research Institute for Cultural Properties ("NNRICP") has continuously undertaken excavation survey research. Furthermore, from 1963, public ownership of the land has proceeded in order to improve the site as a historic site park. With regard to the first imperial audience hall, the NNRICP has implemented related excavation surveys several times, and published an excavation survey report in 1982. In addition, as the part of the total improvement project of the Heijo Palace site, the reconstruction of the first imperial audience hall was planned. After 1989, the first imperial audience hall reconstruction plan commenced its specific review; and, in 1993, the reconstruction principles for the first imperial audience hall were determined. Since then, after the completion of studies and designs for reconstructing the first imperial audience hall, reconstruction commenced in 2001. This work will be completed in March, 2010.
This report explains the studies implemented by the NNRICP including the grounds for reconstruction designs for the first imperial audience hall. The report comprises four volumes, explaining the following items:
1 Platform/Foundation Stone
2 Wooden parts
3 Coloring/clasps and clamps
4 Roof/Rooftiles
While, each volume includes the following content:
I Process of review and creation of report
II Direct data/reference materials relating to the first imperial audience hall of the Heijo Palace
III Case study
IV Process of reconstruction
V Reconstruction plan
The content of the case study indicate details of the basic research implemented in parallel with the reconstruction review. In addition, some findings of studies made after the completion of the reconstruction design are also included. Incidentally, please note that the restoration plan shown in the report only indicates the theoretical form of the ancient architecture, and that the building as it will actually be restored has been changed slightly, taking into consideration factors of structural reinforcement and maintenance.
This report is the first one of these four volumes, explaining mainly the results of studies on the platform and the form/size of the foundation stones.
As previously mentioned, the platform of the first imperial audience hall was largely removed during the late Nara Period. Excavation surveys found that no stone materials used for decoration of the platform remained. However, traces of drawing out the stone material (platform foundation stone; ie, Jifuku-ishi 地覆石) used for the lowest part of the platform and stairs were found, and successfully verified the scale of the lowest part of the platform as well as the position/scale of the stairs. There were six sets of stairs: one in the center of the southern side of the platform, one positioned on each of the east and west sides of the southern platform, and three on the north side. Although the scale of the lowest part of the platform was thus fixed, it was impossible to verify the form and height of the upper part of the platform through excavation surveys. In order to extrapolate the form of the platform, similar examples of architectural structures, excavated structural remains, data of old paintings, etc. of the 7th to 8th century remaining in Japan, as well as case examples of the same period found through excavations implemented in China and Korea were studied.
Furthermore, through studies of similar case examples, not only objects directly related to construction designs, but also those providing an overall picture of techniques used in the construction of the platform in that time period were found. The objects of study and outlines are described below:
1 Study on the foundation stones of the first imperial audience hall, Heijo Palace
We have figured out the form of the foundation stones used at the Heijo Palace by measuring and examining foundation stones excavated mainly from the Heijo Palace. In addition, we researched those of the first imperial audience hall (Kuni Palace), to which the first imperial audience hall of the Heijo Palace was presumably moved, and proved their particularity.
2 Platform and foundation stones of the Kuni Palace
The excavation results of the first imperial audience hall of the Kuni Palace site were reviewed, the form of the platform examined, and the study results thus obtained adopted as data for restoring the inclination of the stairs of the first imperial audience hall. In addition, the properties and shapes of the foundation stones were examined, and the data thus obtained was adopted for reconstructing the foundation stones to be used for the first imperial audience hall. It was also proved, based on the shape of foundation stones, that tuff paving cobbles were used in a pointing, nunoziki style on the platform surface in the ridge direction (lit. fabric paving. In the nunoziki style, a pavement formed by square or rectangular stones is laid so that a little space is allowed around each, the lines formed by the stones running parallel to the edging stones and to each other in a lengthwise direction.).
3 Form and exterior stone materials of the platform faced with hewn stones
As the similar examples of the platforms to the, Examples of platforms using tuff ashlars similar to that of the first imperial audience hall of the Heijo Palace were collected from those of Buddhist temples, dating back to the 7th to 8th centuries, excavated in Nara prefecture. We subsequently examined the form and size of such ashlars used during the period from the 7th to 8th centuries, and calculated the actual size and form of the stone materials used for the platform of the first imperial audience hall.
4 Stairs of platforms
Examples of platforms existing in Japan were collected and organized, and the inclination and form of them reviewed. As a result, despite the prevailing notion that the inclination of stairs is generally 45 degrees, it was proven that many of them are less than 45 degrees. Furthermore, we figured out the construction method of stairs during the period from the 7th to 8th century.
5 Case examples and form of double platform
Examples in Japan of what is called the “double platform” were collected and organized. As a result, it was proven that the lower level of a double platform, with respect to function, is divisible into six types. Furthermore, the studies have indicated the possibility that: (i) the first imperial audience hall of the Heijo Palace belonged to the double platform type; and, (ii) the function of the double platform was likely to have been the pavement for the part onto which raindrops fall from the eaves.
6 Pavement of platform
In addition, with regard to the method of finishing the upper surface of the platform, similar case examples were organized and reviewed. Accordingly, it has been proven that many higher-grade buildings used an ashlar pavement, and that the nunoziki pavement was in general use during the time period above.
7 Platform of Hanyuan Hall (Darning Palace, Chang'an Castle, Tang dynasty) and the 37th hall ruins of Renshou Palace (Sui Dynasty) and Jio Cheng Palace (Tang dynasty)
The excavation results from the Hanyuan Hall site (Darning Palace, Chang’an Castle, Tang dynasty), which was conceivably the model of the first imperial audience hall of the Heijo Palace, as well as those from the 37th hall ruins of Renshou Palace (Sui Dynasty) and the Jio Cheng Palace (Tang dynasty), chronologically-closer to the Heijyo Palace, were reviewed and the construction methods were examined and were conceivably imported from China to Japan during the period from the 7th to 8th centuries.
Based on the studies of similar case examples above, we have undertaken the reconstruction of the platform of the first imperial audience hall. We concluded that the platform was a double platform with the masonry using tuff ashlars, and that the eaves were located above the lower platform (Fig. V-1 to V-5). We also presumed that the scale of the lower platform measured 51.104 meters in the east-west direction, 26.613 meters in the north-south direction, and 1.329 meters in height; while, that the upper platform measured 53.170 meters in the east-west direction, 28.653 meters in the north-south direction, and 1.034 meters in height. The scale of the lower platform was estimated based on excavation results; while that of the upper platform was assessed in light of the overall balance. The inclination of the stairs was evaluated based on the calculation that it is 6/10 (approx. 31 degrees), and on the length of stairs established through excavation surveys. The size of each stone material was determined, consulting those of the main hall of Yakushiji temple, the representative large-scale Buddhist temple architecture of the early eighth century, and taking into consideration the balance of the overall scale.
2009年2月16日 発行
奈良文化財研究所学報 第79冊
平城宮第一次大極殿院の復原に関する研究
