In the 58th year of the Showa period, while investigating the burial grounds during park maintenance an Iron Sword of Bonshin no Toshigokatsu (oldest inscription in Hyogo Prefecture) was discovered. After the park maintenance was completed, the area was named "Tsurugi Gaoka Koen" after the inscribed iron sword. The area was built between the year 630 in the Seireki period and 660. The grave was also seen as a burial ground for important figures such as the Empress Suiko or Prince Shotoku.
In the lower Yagi River area placed by the left bank there are thin valley lines from the north, west and eastern regions that surround the mountains in a bag like terrain. In the narrow area two to five tombs can be found. In the narrow space range 4 ancient tombs numbered 2 through 5 can be found. The second tomb expands 12 meters east to west, and 14m south to north and is a circular shape with raised soil.
The side hole style stone chamber has a length of 9.6 meters, width of 1.2 meters and height of 1.7 meters. The side walls are composed of 3 layers of thin stone slabs. The back walls were thought to have been made by two layers. The third grave is an elliptical shape expanding 9.5 meters east to west and 13.5 meters north to south. The mound has 3 layers of stone pavement. The side hole style stone pavement has a length of 3.6 meters, width of 0.8 meters and height of 0.7 meters. The fifth tomb is a circular tomb, with a diameter of 6 meters, and the stone chamber has a length of 3.6 meters. The burial is a small size perfect for a one-person burial. This location is the first ancient tomb park in Tajima to be declared as Nationally Designated Cultural Property. It continues to represent the Romantic Ancient History of Tajima.
The Boshinen Katana is presently displayed at the Hyogo Prefectural Museum of History. The replica is displayed at the Tsurugi Gaoka Park Gymnasium.
Tsurugigaoka Park 282 Yokacho Koyama-Sugaya, Yabu City