The Ancient Roof Tile Kiln Site at Hidakayama

CONTENTS

Chapter I Introduction　1

　1　Background of the Excavations　1

　2　Organization　2

　3　Preparation of the Present Report　2

Chapter II Previous Research　5

　1　Historical Environment　5

　2　Previous Excavations and Physical Surveys　7

　3　Progress of Excavation Activities　15

　4　Abstract of Excavation Logs　19

Chapter III Archaeological Features　23

　1　Location and Topography of the Site　23

　2　Descriptions of Archaeological Features　23

　　Ａ　Roof Tile Kiln SY11681（ Kiln No. 1） 23

　　Ｂ　Roof Tile Kiln SY11682（ Kiln No. 2） 24

　　Ｃ　Roof Tile Kiln SY11683（ Kiln No. 3） 25

　　Ｄ　Roof Tile Kiln SY11684（ Kiln No. 4） 25

　　Ｅ　Roof Tile Kiln SY11685　26

　　Ｆ　Roof Tile Kiln SY11686　26

　　Ｇ　Roof Tile Kiln SY11687　27

　　Ｈ　Roof Tile Kiln SY11688　27

　　Ｉ　Roof Tile Kiln SY11689　27

　　Ｊ　Pit SK11690　28

　　Ｋ　Diagonal Ditch SD11680　28

　　Ｌ　Features found in the 17th Excavation　28

Chapter IV Artifacts　31

　1　Roof Tiles and Bricks　31

　　Ａ　Roof Tiles from the Kilns at the Hidakayama Site　31

　　Ｂ　Mudbricks from the Kilns at the Hidakayama Site　36

　　Ｃ　Roof Tiles and Mudbricks from the 17th Excavation　40

　2　Pottery and Clay Objects　43

　　Ａ　Pottery from the Kilns　43

　　Ｂ　Pottery from Well SE1850　44

　　Ｃ　Pottery from the East-West Ditch SD1845　45

　　Ｄ　Pottery from the North-South Ditch SD1856　45

　　Ｅ　Pottery and Haniwa from the Diagonal Ditch SD11680　46

　3　Wooden Tablets　47

　4　Wooden Objects　49

　　Ａ　Wooden Objects from the 17th Excavation　49

　　Ｂ　Well Frame of SE1850 from the 17th Excavation　50

　5　Metal Objects　52

　6　Others

Chapter V Scientific Analyses　53

　1　 Wood Species Identification of the Carbonized Materials from the Root Tile Kilns at the Hidakayama Site　53

　2　Radiometric Dating　57

Chapter VI Discussions　63

　1　Structures of the Roof Tile Kilns　63

　　Ａ　Structures of the Roof Tile Kilns at the Hidakayama Site　63

　　Ｂ　Characteristics of the Roof Tile Kilns in the Fujiwara Palace　68

　　Ｃ　Structural Analyses of the Roof Tile Kilns in the Fujiwara Palace　74

　　Ｄ　Roof Tile Kilns in East Asia　77

　　Ｅ　Introduction of Flat Kilns to the Hidakayama Site　82

　2　Production and Supply of Roof Tiles at the Hidakayama Site　86

　　Ａ　 Archaeological Contexts of the Eaves Tiles produced in the Hidakayama Site　86

　　Ｂ　Examination of Eaves Tiles　92

　　Ｃ　Examinations of Concave, Flat, and Tool Tiles　99

　　Ｄ　Production Method of Mudbricks　100

　3　 Characteristics of the Northeast Block of the First Ward, Seventh Avenue, Right Sector　103

　　Ａ　Introduction　103

　　Ｂ　Reorganization of the Results of the 17th Excavation　103

　　Ｃ　Situation of the First Ward, Seventh Avenue, Right Sector　104

　　Ｄ　Situation of the First Ward, Seventh Avenue, Left Sector　105

　　Ｅ　Comparative Study of the Heijo Capital　107

　　Ｆ　Conclusions　108

Chapter VII Conclusions　111

English Summary　115

Interpretation of the Excavated Wooden Tablets　126

Figures

Photographs

English Summary

　The present publication reports the results of the excavations of the roof tile kilns at the Hidakayama site, initiated in 1960 by the Board of Education of Nara Prefecture and subsequently continued through the Fujiwara Palace 23-7th excavation in 1978 and Asuka-Fujiwara 213th excavation in 2023, both conducted by Nabunken. This chapter summarizes the historical significance indicated by the excavations of the roof tile kilns at the Hidakayama site.

1 ．Extent and Period of the Hidakayama Site

　The Hidakayama site, comprising ancient roof tile kilns, extends approximately 50 meast-west along the northern slope of the eastern ridge of Hidakayama Hill, immediately south of the Fujiwara Palace. Its location, directly facing the palace, was particularly wellsuited for supplying roof tiles for the palace construction and clearly distinguishes the site from the other kiln sites.

　To date, a total of nine kilns have been identified through the excavations conducted by the Board of Education of Nara Prefecture in 1960（ n = 1 ）, by Nabunken in 1978（ n = 2 ）and in 2022（ n = 6 ）.

　Excluding unexcavated （SY11683 and 11687） and unfinished kilns （SY11688）, the excavated kilns consist of three anagama kilns （SY11681, 11686, and 11689）, two flat kilns （SY11682 and 11684）, and one hybrid type combining characteristics of both anagama and flat kilns （SY11685）. The chronological relationships among these kilns can be partially reconstructed. For example, the ash deposit of SY11685 was cut by a pit for the construction of SY11686 （see Section III. 2 ）. Traces of two episodes of heat exposure in SY11681 suggest that kilns were constructed twice at the same location （see Section VI.1 ）. The fact that these nine kilns were generally constructed without overlapping one another supports the interpretation that they were in operation during the same period.This chronological framework is further corroborated by the eaves tiles recovered from the kilns, which are classified into the same typological groups（ see Section VI. 2）.

　The roof tiles recovered from canal SD1901A in the lower layer of the Fujiwara Palace,produced at the Hidakayama site, provide crucial evidence for determining the construction period. The lowest layer of the canal yielded wooden tablets bearing dates between AD 682 and 684, as well as a reference to the official title of "Shindaishu," established in AD 685. On this basis, the excavation context of SD1901A is dated to the reign of Emperor Tenmu, that is, the latter half of the seventh century AD1）. Accordingly, the establishment of the roof tile kilns at the Hidakayama site most likely dates to this same period. Chapter VI presented the results of radiometric dating of excavated carbonized materials, indicating a date range from the end of the seventh to the beginning of the eighth century AD. Taken together,these results suggest that the roof tile kilns at the Hidakayama site were established at the earliest stage of construction of the Fujiwara Palace.

2 ．Characteristics of the Kiln Structure

　As mentioned in Chapters III and VI, previous research has revealed that the roof tile kilns at the Hidakayama site adopted structural characteristics that differ from those of the other kilns established during the construction of the Fujiwara Palace. The most notable feature is the introduction of flat kilns.

　Notably, the Hidakayama site yielded two flat kilns dating to the end of the seventh century AD, although the introduction of the flat kilns is conventionally dated after the mid-Nara period（ eighth century AD） in the history of Japanese roof tile kilns. In addition to their early date, these flat kilns are characterized by the use of mudbricks as construction material. Nevertheless, variations are observed in their construction method; SY11684 did not use backfill soil, whereas SY11682, which had a more extensive construction pit, was built with partial backfill behind the mudbrick wall.

　The three anagama kilns at the Hidakayama site also represent a structure distinct from the anagama kilns that became prevalent in Japan after the latter half of the sixth century AD, when domestic roof tile production began. These anagama kilns are characterized by large construction pits designed to accommodate massive rammed-earth foundations.To date, no comparable structures have been identified at other kiln sites producing roof tiles for the Fujiwara Palace or at sites dating to the Nara period and later. This situation suggests that the construction techniques introduced at the Hidakayama site were not widely standardized, although the functional advantages of this particular structure remain unclear.

　Furthermore, the excavations identified the hybrid kiln type （SY11685） combining characteristics of both anagama and flat kilns, representing the first such example documented to date. This finding indicates that interactions between conventional and advanced techniques occurred during kiln operation. Specifically, the anagama kilns SY11681 and SY11686 were constructed entirely using mudbricks, while the flat kiln SY11682 adopted a rectangular installation plan comparable to that of the anagama kilns.

　In summary, the roof tile kilns at the Hidakayama site constitute a significant case illustrating an incipient stage of kiln operation during the construction of the Fujiwara Palace. The site demonstrates the introduction of flat kilns, representing the most advanced technique in the period, in combination with conventional anagama kilns. These findings provide an important opportunity to re-examine technological change in the roof tile production from the end of the seventh century AD onward.

3 ．Production and Supply at the Hidakayama Site

　At the Hidakayama site, nine roof tile kilns constructed using both conventional and advanced techniques were newly put into operation for the construction of the Fujiwara Place. This situation suggests that a large-scale production system capable of supplying an enormous quantity of roof tiles had already been established at an early stage of the palace construction.

　A total of four types and eight subtypes of round eaves tiles （6233Aa, Ab, Ac; 6274Ab, Ac;6275E, I; and 6279Aa）, as well as a single type of flat eaves tiles（ 6643Aa）, were produced in the roof tile kilns at the Hidakayama site. Prior to the 213th excavation, only type 6274Ab had been identified within the kilns at the site, while the other types were recovered from the east-west ditch SD1845 during the Fujiwara Palace 17th excavation. The 213th excavation revealed the full range of roof tile types produced at the site, including four types and six subtypes of round eaves tiles and a single type of flat eaves tiles. Given that multiple types were recovered from individual kilns, while a single type was produced in multiple kilns, production does not appear to have been specialized by roof tile type within individual kilns（ see Section VI. 2 ）.

　As described in Section VI. 2, eaves tiles produced at the Hidakayama site were primarily used for the perimeter wall and gates of the Fujiwara Palace, whereas only a small number were recovered from the imperial audience hall and the state hall located at the center of the palace complex. This distribution suggests that construction of the Fujiwara Palace began with the perimeter wall and subsequently proceeded toward the central sector, where roof tiles produced at the Kodai and Minedera kiln sites were predominantly used. Furthermore, molds for eaves tiles （6274Ac, 6279Ab, and 6643Aa） were transferred from the Hidakayama site to the Kodai and Minedera sites, indicating that these latter sites likely assumed the continuous production following the abandonment of the Hidakayama site. Both the timing of this mold transfer and the cessation of kiln operation at the Hidakayama site correspond closely to AD 684, when palace construction was interrupted by the death of Emperor Tenmu. The abandonment of the unfinished kiln SY11687, identified in the present report, can be interpreted within this historical context.

　Despite the relatively short duration of operation, the roof tile kilns at the Hidakayama site were established as part of an intensive, integrated production system involving multiple kiln sites during the early stage of the construction of the Fujiwara Palace.

4．Transition and Transmission of Roof Tile Production Technology in Ancient East Asia

　To date, the flat kilns at the Hidakayama site have been regarded as the earliest examples in Japan. Despite the existence of numerous kiln sites in western Japan that supplied roof tiles to the Fujiwara Palace, no other site has introduced flat kilns. Under these research circumstances, scholarly attention has focused on the background to the appearance of flat kilns at the Hidakayama site.

　Across East Asia as a whole, semi-downdraft flat kilns had been traditionally operated in China since the Western Zhou dynasty. A comparative study has pointed out similarities between flat kilns in China and those at the Hidakayama site 2） . Based on roof tile production techniques at the Hidakayama site and other kiln sites associated with the palace construction－specifically, the use of clay strips applied to tubs or wooden frames－previous research suggested cultural influence from China3）.

　After summarizing contemporaneous kiln sites in China and South Korea, Section VI.1 discussed similarities and differences between the Hidakayama site and those sites.Despite similarities in overall form and structure, significant differences are evident. Flat kilns in China and South Korea were fully subterranean constructions, whereas those at the Hidakayama site exhibit a semi-subterranean form. The methods of mudbrick use also differ among these regions. A structural similarity is observed in the chimney design between the Hidakayama site and the Teiwari kiln site in South Korea, while the overall kiln structure at the Hidakayama site is more comparable to Chinese kilns of the Wei, Jin, Northern and Southern Dynasties than to those of the Tang Dynasty. In principle, the flat kilns at the Hidakayama site were likely constructed under Chinese influence. However, pronounced variation in interior kiln structures indicates that direct technological transmission did not occur at the Hidakayama site, even though general structural characteristics were shared with Chinese kilns.

　Considering the historical context, the interruption of Japanese envoys to the Tang Dynasty resulted in a stagnation of relations with China during the 680s, the period during which the Hidakayama site was in operation. Accordingly, direct transmission of flat kiln technology from China must be evaluated with caution.

　If indirect technological transmission via the Korean Peninsula is assumed, flat kilns in the Teiwari site in Baekje, which are contemporaneous with or slightly earlier than the Hidakayama site, nevertheless display marked differences in detailed structure, despite a limited number of similarities. To date, no flat kilns have been identified in the Silla region. On this basis, technological transmission via the Korean Peninsula is difficult to substantiate.

　At present, the flat kilns at the Hidakayama site are most plausibly interpreted as having originated from China. Although the routes and circumstances of their introduction remain unclear, differences between flat kilns at the Hidakayama site and Chinese examples suggest a selective and adapted adoption based on partial knowledge rather than the formal introduction of standardized technology. As these imitated flat kilns may not have achieved the expected production capacity, this kiln type was likely not adopted at other kiln sites supplying roof tiles for the Fujiwara Palace.

　In conclusion, the flat kilns at the Hidakayama site provide important insights into the processes of technological transmission in roof tile production across East Asia. Including the Korean Peninsula, the technological genealogy and pathways of transmission should be further contextualized through comparative studies of roof tile kilns from the Tang Dynasty.

5 ．Concluding Remarks

　The roof tile production system at the Hidakayama site is characterized by the introduction of continental technology for the first construction of a roofing palace in Japan,accompanied by continuous technological experimentation.

　The Hidakayama site is distinct from other kiln sites that produced roof tiles for the Fujiwara Palace in that it exhibits the coexistence of anagama and flat kilns, as well as the presence of hybrid kilns combining features of both types, indicating an incipient stage of technological experimentation. Moreover, the location of the Hidakayama site directly in front of the Fujiwara Palace--a configuration unparalleled among other kiln sites--reflects an expectation that the site would play a central role in supporting roof tile production for the full-scale construction of the palace, drawing upon advanced technology derived from China. This intention is partly evidenced by the transfer of eaves tile molds to the Kodai and Minedera kiln sites, which became subsequent production centers following the abandonment of the Hidakayama site.

　Accordingly, the Hidakayama site and the results of the excavations hold significant historical value, not only for understanding a component of the roof tile production system associated with the first construction of a roofed imperial palace in Japan, but also for elucidating the processes of transition and transmission of roof tile production technology in ancient East Asia within their broader historical context.

Notes:

1 ） Ishida, Y. 2012 Roof Tile Production in the Fujiwara Palace and its Date. In Nara National Research Institute for Cultural Properties （ed.）, Advances in the Study of Cultural Properties, Vol. 4. Pp. 317-344. Nara: Nara National Research Institute for Cultural Properties.（ In Japanese）.

2 ） Mukai, Y. 2024 Structure of Roof Tile Kilns before the Tang Dynasty, China. In Society for the Study of Kiln Sites （ed.）, Studies of the Structure of Roof Tile Kiln. Pp. 291-306.Kyoto: Shinyosha.（ In Japanese）.

3 ） Sagawa, M. 1992 Examination of Forming and Decoration Techniques of the Chinese Flat Eaves Tiles: A Comparative Study of the Production Technology of Roof Tiles in East Asia. Bulletin of Japan Society for Chinese Archaeology 2 : 1 -13.（ In Japanese）.