The tumulus group was designated a National Historic Site in 2013, with the area under protection expanded in 2014.

[1] The National Historic Site consist of nine burial mounds that were built from the early Kofun period to the early middle Kofun period in an area of 4.5 kilometers east–west and 3.5 kilometers north–south centered on the coastal area of Tsuda Bay overlooking the Seto Inland Sea.

This group of burial mounds was known in the Edo period, and there are records of archaeological excavations from the early twentieth century onwards.

The split bamboo-shaped sarcophagi at the Tsuda Kofun cluster was made from volcanic stone produced in this area, and the same volcanic stone sarcophagus have been found in the Kinai, Kibi, and Awa regions, which suggests a strong maritime connection.

In the middle of the Kofun period, when the Tomita Chausuyama Kofun, the largest keyhole-shaped burial mound in Shikoku, appeared inland, the construction of burial mounds in the Tsuda site stopped.