The tamagawadai Kofun Gun is located on an elongated plateau on the left bank of lower Tama River, the tomb mounds in the group were constructed between the Kamenokooyama Kofun designated by the state on the south side and the Horaisan Kofun designated by the Tokyo Metro Gov. on the north side.
The group consist of a total of eight tomb mounds, which all are identified as being from the Late Kofun Period (the first half of 6th to the middle of the 7th century). Excavations were conducted in 1957 and 1958, and investigations for confirmation were pursued from 1987 to 1991. Based on the results of these investigations, it appears that a circular tomb mound defined as Tomb Mound No.2 was first built about the first half of 6th century, and subsequently a keyhole-shaped tomb mound, Tomb Mound No.1 which made use of Tomb Mound No.2 as its own circular mound portion was constructed in the second half of 6th century. Later Tomb Mounds No. 3 to 6 were built, further mounds of small size from 15 to 19m in diameter, are concentrated, therefore called densely-gathered tomb mounds.
Excavated relics from the stone chambers of some of these tomb mounds are as follows: weapons like straight swords and iron arrow heads as burial accessories, ornaments like earrings and cylindrical beads, bits for horses, Haji wares and blue-gray pottery.
While many of groups of tomb mounds which existed before in the Metropolitan area have passed into obscurity time of their construction is a valuable group of tomb mounds.
(Tokyo Metropolitan Board of Education)