The Tumulus cluster dates back to the latter of the Kofun (tumulus) period (250 - 538). Excavations unearthed horse tack like bits for horses, Sue ware (type of unglazed pottery made from the middle of the Kofun era through the Heian era), Haji ware (plain, unglazed, reddish-brown Japanese pottery made from the Kofun era through the Heian era), and haniwa (clay figures from the Kofun period).
The Tamagawa-dai Tumulus Cluster is a group of ancient burial mounds consisting of eight tumuli. It is estimated that these burial mounds were created between the early 6th to the mid-7th century consecutively. Excavation efforts from the tumuli unearthed weaponry such as chokuto (straight swords from pre-10th century Japan), iron arrowheads, ornaments such as earrings and kudatama (cylindrical jewels), horse tack such as bits and Sue and Haji ware, which were buried together in the tunnel-shaped stone chamber, and Haniwa (cylindrical clay figures) were discovered in the mound itself. The Tamagawa-dai Tumulus Cluster is a part of the Ebara-dai Tumulus Cluster. Many of the tumuli of of the Ebara-dai Tumulus Cluster have been lost due to urban development. The remaining tumuli have a historical significance not only because they retain the original shape, but they also give an idea of how the graves of regional chiefs in the lower reaches of the left bank of the Tama River at that time changed with the course of time. The view is great too. On a sunny day you can see the Tanzawa Mountains and Mount Fuji. It is also selected as one of the ”Eight Great Views of the Tama River”. In 2000, it was designated as one of the Tokyo Metropolitan Area - Designated Ancient Sites. It is a one-minute walk from ”Tamagawa” Station of the Tokyu Tamagawa Line