The Satadani-Satadao group of graves with burial mound, where the excavations were carried out, is located at the urban area on the east side of Shōbara city in the northern part of Hiroshima Prefecture. The group was built between the end of the last third of the Middle Yayoi period (1st century BC) and the first third of the Late Yayoi period (1st century AD).
A series of excavations yielded the following results: Satadani grave No. 1 and 2, Satadao grave No. 3 are graves with rectangular burial mound and four corner projections (yosumi tosshutsugata funkyū bo); Satadao grave No. 4 has also a rectangular burial mound with four corner projections, but it has subsequently been modified and altered into a square-shaped burial mound; Satadani grave No. 3, Satadao grave No. 1 and 2 are square-shaped ditch-enclosed slightly elevated burial precincts (hōkei shūkō bo); Satadao grave No. 5 is a square-shaped ditch-enclosed slightly elevated burial precinct (hōkei shūkō bo), where on the inside of the ditch-enclosed space a grave pit was confirmed.
One important result of this investigation was the discovery of variations in Yayoi burial mound construction techniques. Towards the end of the last third of the Middle Yayoi period after repeated burials of several individuals, the burial mound of the Satadao No. 3 grave was completed. In other words, it became clear, that at the grave No. 3 with rectangular burial mound with four corner projections, grave pits were first excavated before the burial mound was finally taking shape. Then the deceased persons were buried within and thereafter the grave pits were backfilled with the soil of the pit excavation. The so repeated iterations of grave pit excavation, burial and backfilling gradually produced the mound. However, on the other hand at Satadani grave No. 1, Satadao grave No.1 and 2 the burials took place after the earthworks of the mound were nearly completed.
According to the results of the surveys, within the same group of graves one could confirm that the construction methods of the burial mounds changed: from the type, where the mound and the burial facilities are simultaneously constructed (“concurrent progression” type) of the end of the last third of the Middle Yayoi period to the type, where burial mound construction proceeds first (“mound first” type) of the first third of the Late Yayoi period. It became clear that this is a rather rare group of
graves with burial mound.
Due to our research it became clear that from the San’in region to the Chūgoku mountain range, a type of burial – termed here, the “mound last” type – can be found, wherein an earth mound was constructed only after digging the grave and completing the burial. The “concurrent progressive” types, referred to previously, were common in the Middle Yayoi period stage. The “mound-first” type noted at Satadani grave No. 1 appeared in the Late Yayoi period. These elements were adopted in large or huge burial mounds in other regions. This empirical evidence demonstrates that changes in burial mound construction methods were a catalyst for the changes in burial rites – concerning their scale and magnificence on the occasion of burials of chiefs.
In Satadani burial mound No. 3, small grave pits are distributed at the lower level of the mounding, revealing that burials were continually taking place there while the mound was being formed. Furthermore, a large grave pit over 6m in length, which constitutes the principal burial chamber, was detected in the upper mounding along with shafts and other burial facilities, and part of this pit was revealed to be overlapping with another grave pit which constitutes a peripheral burial chamber. It is therefore plausible that this burial mound can be classified as an “eclectic” style that mixes together the “concurrent progressive” and “mound-first” styles. Moreover, two pieces of earthenware were unearthed: vermilion-lacquered vessels with spout and large attached pedestal foot. These were products of the technology of the southern part of Okayama Prefecture. Interestingly, they have holes knocked into them. This feature conjures up an image of the subsequent ceremonial vessel stand (tokushu kidai), which later evolved into the cylindrical clay figures (entō haniwa) of the Kofun period).
The Satadani burial mound group is the place where funeral rituals first started to involve a combination of elements such as the following: A wooden chamber (mokkaku) housing a wooden coffin is interred within the burial pit and then large red-colored pottery (like vessels with attached pedestal foot, chūkō kyaku tsuki bachi) are offered at the surface of the grave pit; round pebbles or stone slabs are distributed around the grave to serve as markers, which were become used with offering pottery in the Late Yayoi period; and the graves are arranged in such a way that a large grave pit constituting the main burial is surrounded by other smaller burials in its vicinity at the top of the mound. These elements of ritual (facilities, implements and process of the burial, etc.) are the origin of the elements of the funerary ritual observed in the large and giant Yayoi burial mounds that developed from the last third of the Late Yayoi period onward in the eastern part of Shimane Prefecture, the southern part of Okayama Prefecture, and the northern part of Kyōto Prefecture.
The results of the research have provided further confirmation of the Satadani burial mound group’s forerunner-status in the development of Yayoi burial mounds. The site vividly displayed the transformation in Yayoi burial mounds that occurred from the Middle Yayoi period to the Late Yayoi
period.
Thus, we identify the Satadani-Satadao burial mound group as an extremely important archaeological site for studying the development, in terms of appearance and increase in size, of the Yayoi-period burial mounds. This group is not only constructed during a relatively early stage of Yayoi period graves with burial mound, but also it became obvious that this a very important site, if one is taking into consideration the development of burial mounds of Yayoi period graves.
In addition, this study incorporates the interrelation of burial mound construction methods and funeral rites, thus making it a fundamental investigation from a comparative archaeological perspective regarding the research of burial mounds not only in Japan, but also overseas.