Oyamato Tomb Group (大和古墳群)
The Oyamata tumulus group is located in the southern part of Tenri City of Nara Prefecture
From the south, the three tumulus groups of the Makimuku tumulus group, the Yanagimoto tumulus group, and the Oyamato tumulus group are located along the southeastern foot of the Nara basin. Though classified into the three groups, they can also considered constituting a tumulus group. Furthermore, excluding the Makimuku tumulus group (or also called Hashinaka tumulus group) that includes the Hashihaka tumulus, one of the oldest keyhole-shaped tumuli, the two groups of Oyamato and Yanagimoto, which are considered having been constructed later, can be integrated into the Oyamto/Yanagimoto tumulus group.
The construction sites of huge tumuli, being presumed those of emperors, moved to the northwestern part of the Nara basin in the later era of the first half of the kofun period. It is the Sakitatenami tumulus group.
The name of the Oyamato tumulus group originates in the fact that Oyamato-jinja Shrine is located on the western side of the tumulus group. This group includes 12 keyhole-shaped tumuli, five zenpo-koho (square front, square back) tumuli, and seven round tumuli. These tumuli can be further classified into the Nakayama sub-group that consists of the tumuli on the hill and the Kayo sub-group that consists of the tumuli on the alluvial fan.
Since there is no much difference among the tumuli in the Oyamato group, no relationship between a main tumulus and its secondary tumulus exists among them. In the Yanagimoto group in the south, the tumuli have a tendency of consisting of main tumuli and their subsidiary tumuli, and the Makimuku group consists of main tumuli and their subsidiary tumuli. Here, a subsidiary tumulus does not mean that the person buried there was forced to die following the death of the person's master.
The Nishi-Tonozuka tumulus (234m), the largest keyhole-shaped tumulus of the Oyamato group, may have been constructed earlier than the Andonyama tumulus (the present mausoleum of Emperor Sujin, 241m) and Shibutani Mukoyama tumulus (the present mausoleum of Emperor Keiko, 310m).
Because the Nishi-Tonozuka tumulus is managed by The Imperial Household Agency, no scholar as well as ordinary persons can enter the tumulus site.
The Nishi-Tonozuka tumulus, the largest one of the Oyamato group described above, is considered being the tumulus of an Emperor-class person. The Higashi-Tonozuka tumulus as long as 175m is located in the neighborhood. In addition, seven 100m to 140m keyhole-shaped tumuli and three zenpo-koho tumuli exist there as well. This group also includes the 120m Nakayama Otsuka tumulus (designated as a historical site by the prefecture), where broken pieces of a tokushu-kidai (ceremonial vessel stand) specific to the Kibi area were found in 1986, and based on the discovery, it was pointed out that the tumulus may have been constructed in the era when kofun tumuli started being constructed. In addition, it was found in 1993 that a vertical style stone chamber existed in the round part of this tumulus. Stone plates supposed to be pyroxene andesite (sanukite) are mainly used for this stone chamber. The Shimoikeyama tumulus there is also designated as a historical site by the prefecture.