Investigation of a subterranean tomb in Miyazaki, Japan

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  • Investigation of a Subterranean Tombin Miyazaki, Japan

    WALTER EDWARDS,1* MASAAKI OKITA2 AND DEAN GOODMAN3

    1Department of Japanese Studies, Tenri University, Tenri, Nara 632-8510, Japan2Department of Archaeology, Tenri University, Tenri, Nara 632-8510, Japan3Geophysical Archaeometry Laboratory, University of Miami Japan Division,

    Otsubu 39-1, Nakajima Machi, Ishikawa 929-2200, Japan

    ABSTRACT A subterranean chamber tomb in Miyazaki, Japan was investigated in an experimental pro-gramme combining remote sensing, excavation and scientific analysis of the materials recovered.Ground-penetrating radar (GPR) was used to locate the tomb, for which no visible surfacemarkers remained. The approach to the tomb was then excavated to expose the sealed entranceto the burial chamber, through which a small hole was bored for the insertion of a miniature videocamera. Based on the images thus obtained, the cooperation of specialists was enlisted for theanalysis of substances expected to be recovered from the chamber, and plans were made forthe collection of suitable samples. This strategy permitted the identification of docosahexaenoicacid, a fatty acid characteristically found in fish and shellfish, in the residue from a dish whichappeared in the video to be lying in its original position, demonstrating the utility of obtainingvisual images by non-destructive means prior to full-scale excavation. Other results from theexcavation similarly provide a means for evaluating the utility and accuracy of the various remotesensing methods used (GPR, resistivity and ground temperature surveys, visual inspection byminiature video camera and fibrescope). Copyright *c 2000 John Wiley & Sons, Ltd.

    Key words: ground-penetrating radar; remote sensing; video; ground temperature measure-ment; Kofun period; Japan

    Introduction

    Burial mounds appeared in the Japanese archi-pelago during the fourth to third centuries BC,and continued to be built until the eighth centuryAD. Within this interval, mounds having adistinctive keyhole shape were constructed fromthe third through the sixth centuries AD, a timeknown as the Kofun period. With the diffusion ofcorridor-style stone chambers from the Koreanpeninsula in the fifth century AD, the shape offacilities for interring human remains underwent

    great change, as did burial practices as a whole.For example, whereas burials were previouslypositioned within the fill of the mound, corridor-style stone chambers came to be built with theirlower portions set directly into the natural strata,and their upper portions covered over with fill.Shortly after the introduction of these stonechambers, corridor-style tombs appeared inwhich the entire burial chamber was dug directlyinto the ground. Because the approach to theentrance of such a tomb is basically either level(or on an upward incline), as when the chamberis tunnelled into a steep slope (Figure 1a), or inthe form of a vertical shaft, as when the tomb isdug below the ground level (Figure 1b), thesegraves traditionally have been divided into twotypes, horizontal chamber tombs and subterra-nean chamber tombs, respectively (Sait o, 1961).

    Copyright # 2000 John Wiley & Sons, Ltd. Received 6 July 1999Accepted 29 October 1999

    Archaeological ProspectionArchaeol. Prospect. 7, 215224 (2000)

    *Correspondence to: Dr Walter Edwards, Department ofJapanese Studies, Tenri University, Tenri, Nara 632-8510,Japan. Email: edwards@sta.tenri-u.ac.jp

    Contract grant sponsor: Japanese Ministry of Education,Grant-in-Aid for Scientific Research in Priority Areas.

  • Whereas the former is distributed widelythroughout Japan, the latter is limited to thesouthern island of Kyushu. Recently, a style ofgrave combining aspects of both types, in whichthe approach is dug on a downward incline fromthe ground surface (Figure 1c), has been dis-covered in Miyazaki Prefecture, on Kyushussoutheastern coast (Hidaka, 1995).

    The current contribution reports the invest-igation of such a tomb, located in Miyazaki andbelonging to this new type, whose downwardinclining approach had been partially filled at thetime of burial. As natural sedimentation pro-ceeded, the position of the approach could nolonger be discerned from the surface, and in theabsence of a mound or scatterings of funerarypottery to serve as markers, knowledge of thegraves existence was lost. As long as such gravesremain relatively intact, the tombs sealedchambers present large subterranean cavitiesthat are easily detected by prospection, especiallyground-penetrating radar (GPR). Moreover, thesoils of Miyazaki are characterized by wide-spread deposits of volcanic ash, which experiencehas shown to yield good results with GPR.Accordingly, these conditions were consideredideal for an experimental programme of investi-gation in which GPR and other forms of remotesensing were used to obtain as much informationas possible prior to excavating the chamber of theparticular grave examined. These data were usedto devise an optimum strategy for the excavation,which in turn yielded results that provide a

    means for evaluating the utility and accuracy ofthe remote sensing methods used.

    Archaeological prospection andexcavation of the SaitobaruTomb Cluster Site

    Prospection was conducted at the Saitobaru TombCluster Site, in a location where the existence ofchamber tombs having either level or downwardinclining approaches had been ascertained prev-iously through archaeological investigation. TheSaitobaru Site lies atop a tableland spreadingapproximately 2 km eastwest and 4 km northsouth, where more than 300 tombs of variousshapes and sizes were built from the fourththrough the sixth centuries. Three seasons ofwork, combining prospection and excavation,were conducted in the following manner.

    First season (survey and prospection),JulyAugust 1995

    The Sakamoto-no-ue precinct of the SaitobaruSite, which had been partially excavated byMiyazaki Prefecture and the local city of Saitoin conjunction with the planned construction of aroadway (Miyazaki Ken and Saito-shi Ky oikuIinkai, 1996), was selected for prospection, pre-ceded by a topographic survey. Radar andresistivity surveys were conducted first in SectorA, where excavation had uncovered portions ofsix downward inclining approaches to subterra-nean chambers (Figure 2). The chambers them-selves, anticipated on the basis of archaeologicalinference, were picked up clearly with radar,although results from the resistivity survey couldonly be marginally interpreted as indicating thesefeatures. Whereas reasons for the poor responsein the resistivity survey are thought to becomplex, the extremely arid condition of thesoil was probably a factor.

    The radar survey was extended to the adjoin-ing Sector B, in order to search for as yetundetected graves, and anomalies were pickedup at three points. One of these later proved to bea layer of sand lining the bottom of a trench fromthe earlier excavation. The other two anomalies,

    Figure 1. Types of corridor-style chamber tombs, differ-entiated by shape of the approach: (a) horizontal (orupward incline), (b) vertical, (c) downward incline.

    216 W. Edwards, M. Okita and D. Goodman

    Copyright # 2000 John Wiley & Sons, Ltd. Archaeol. Prospect. 7, 215224 (2000)

  • labelled X1 and X2, were judged to representhollow chambers sharing a single approach, withX1 lying deeper than X2 (Figure 3a). Thesefeatures were given the label of Tomb 7, althoughit could not be judged at this point whether theapproach was of the same downward incliningtype as observed for Tombs 16. Measurementswere taken of the ground temperature 20 cmbelow the surface at a point above the inferredlocation of chamber X1, and at points distantfrom it. From the onset of measurement at

    8:45 am until 11:00 am, the temperature at thepoint above the chamber measured between 0.4and 1.78C lower than points away from it, but bynoon significant differences in temperature wereno longer observed.

    Second season (prospection and partialexcavation of Tomb 7), December 1995

    Based on the radar profiles of Tomb 7, and ontime-slice maps (Goodman and Nishimura, 1993;

    Figure 2. Sakamoto-no-ue precinct, Saitobaru Tomb Cluster Site.

    Subterranean Tomb in Miyazaki, Japan 217

    Copyright # 2000 John Wiley & Sons, Ltd. Archaeol. Prospect. 7, 215224 (2000)

  • Figure 3. The GPR data for Tomb 7, Saitobaru Tomb Cluster Site: (a) 15th northsouth profile (see Figure 2 for position),showing anomalies X1 and X2 and their estimated depths, (b) time slice at approximate depth window of 240288 cm.

    218 W. Edwards, M. Okita and D. Goodman

    Copyright # 2000 John Wiley & Sons, Ltd. Archaeol. Prospect. 7, 215224 (2000)

  • Goodman et al., 1995) made by Dean Goodman(Figure 3b), the chamber of X1 was judged to be acavity having a roughly rectangular shape andmeasuring between 2.1 and 3.1 m northsouth by1.8 to 2.8 m eastwest. Ground temperaturemeasurements, taken in the same manner asdescribed above, showed that the subsurfacetemperature directly above the X1 chambercontinued to measure lower than at other points,even in the winter season. Using this result, anattempt was made to infer the size of thechamber of X1 using ground temperaturemeasurements alone, yielding an estimate ofapproximately 3 m northsouth by somewhatless than 3 m eastwest.

    After locating with radar the position of theapproach to the graves, the topsoil was removedfrom an area roughly 15 m northsouth by 9 meastwest, in which the outline of the filled-inapproach was detected, and its northeast quad-rant then excavated (Figure 2). The entrance ofthe corridor leading into the chamber of X1 waslocated with its floor at 2.8 m below the groundsurface, and that of X2 similarly located at adepth of 2.1 m, confirming the inferences basedon radar profiles th