According to the 1969 investigation report regarding the “Shijikkan-kohara” which was excavated a year earlier, it comprised a series of pit graves (dokō bo) from the Yayoi period. However, a more recent reinvestigation of this site suggests instead that a rectangular-shaped grave with multi-row stone pavement on the slope of the burial mound (hōkei hariishi bo) is the case here. Therefore, “Shijikkan-kohara” has been re-defined as a Yayoi period grave with burial mound (yayoi funkyū bo).
It was constructed in the last third of the Middle Yayoi period and contained five burial facilities. These facilities, including some for children, were built prior to the construction of the burial mound. According to this fact, it was built using the so-called “mound last” method, where the burial mound construction is carried out at the end, after the burial facility is dug out respectively erected (funkyū kōkōgata; “mound last” construction type).
The ways through which one constructed the mound and the stone pavement and arranged the burials, were also investigated. Similarly, the Narahama Yayoi period burial mound group and the Umeda-kayamine burial mound in the Chūgoku region were both constructed using the “mound last” method. As both of them were built during the Middle Yayoi Period, one could shed light on the development of the construction method concerning the relationship between the burial facilities and the mound. It changed from the “mound last” type to “concurrent progression” type (here, the mound and the burial facilities are simultaneously constructed) to the “mound first” construction type, where the piling up of the burial mound proceeds first. In addition, it concerns the stone pavement at the mound base as well as boundary stones (hyōseki) on top of the grave pits such as stone alignments enclosing or paving the grave (haiseki) and arrangement of the the burials are indicating an initial type. This can be considered them as an ancestral form of Yayoi burial mounds in the Chūgoku region. Also the possibility can be assumed that this situation developed from burials practices which were already present in the San’in region and the Chūgoku mountainous regions during the first half of the Yayoi period.
Accordingly, the “Shijikkan-kohara” Yayoi period burial mound is an important archaeological site for studying the origin and evolution of such graves with burial mounds during the Middle Yayoi period in the Chūgoku region.