Ōmaruyama Kofun

Ōmaruyama Kofun is a 4th century Kofun period burial mound in the Nakamichi neighborhood of Kōfu, Yamanashi, in Japan’s Chūbu region. It stands on the southeastern edge of the Kōfu Basin, along a ridge of a 310 meter mountain above the Chōshizuka Kofun - Maruyamazuka Kofun. The mound was designated a National Historic Site of Japan in 2013.

The tumulus is a keyhole-shaped zenpō-kōen-fun, with a square end and a circular end when viewed from above. It measures 105 meters overall and follows an east-west axis. Its circular rear portion is 48 meters in diameter, while its rectangular front portion is 34 meters wide. No haniwa or fukiishi have been found.

Excavations in 1970 and 1976 uncovered a burial chamber with a two-tied structure measuring 2.2 meters long and 0.8 meters wide. Its interior was painted in vermillion. The chamber held the remains of two adult men and women, together with iron armor, weapons, swords, agricultural implements, three bronze mirrors, beads and jewelry. Many artifacts are preserved at the Tokyo National Museum.

Ōmaruyama Kofun was discovered in 1920 and is dated stylistically to 301 CE to 400 CE. One bronze mirror, the Shinju-kyo, matches mirrors found at the Uchikoshi Kofun in Gifu and the Teradani Chōshizuka Kofun in Iwata, Shizuoka. Kofun are the great burial mounds of ancient Japan, built mainly between the middle of the third century and the early seventh century CE; keyhole-shaped mounds are their most distinctive form.

The Ōmaruyama Kofun is located on the southeastern edge of the Kōfu Basin on the ridge of a 310 meter mountain which extends to the left bank of the Fuefuki River. The area has a high concentration of Kofun period remains and is located immediately above the Chōshizuka Kofun - Maruyamazuka Kofun. The Ōmaruyama Kofun was discovered in 1920, and is a zenpō-kōen-fun (前方後円墳), which is shaped like a keyhole, having one square end and one circular end, when viewed from above. It has an overall length of 105 meters, and is aligned in along an east-west axis, taking advantage of the natural topography. The posterior circular portion has a diameter 48 meters, and the anterior rectangular portion has a width of 34 meters. No haniwa or fukiishi have been found.

The site was excavated in 1970 and again in 1976, during which time the burial chamber was uncovered and found to be a peculiar two-tied structure with length of 2.2 meters and width of 0.8 meters. The interior of the sarcophagus was painted in vermillion, and contained the remains of two adult men and women along with many burial goods. These included an almost intact set of armor made from iron plates, iron weapons and swords, agricultural implements, three bronze mirrors, beads and jewelry. One of the bronze mirrors, or Shinju-kyo was of especial interest, as it was identical to mirrors found at the Uchikoshi Kofun in Gifu and the Teradani Chōshizuka Kofun in Iwata, Shizuoka. Many of the excavated artifacts are now preserved at the Tokyo National Museum.