Tsukuriyama Kofun 造山古墳, located in Okayama city, Okayama prefecture, is a zenpoukouenfun 前方後円墳 measuring approximately 350 meters in total length and dating to the early 5th century; it is the fourth largest kofun in Japan.
Okayama University announced on March 17, 2010, that the remains of a moat surrounding the tumulus had been uncovered. The find is drawing considerable attention as it not only confirms that the chieftain of the area now Okayama — the ancient kingdom of Kibi (吉備地方) — held comparable power as the Kinki Great King, but also built its giant tombs in roughly the same manner. The kingdom of Kibi, which centered on the current Okayama, possessed a distinct culture from the nearby Yamato dynasts and remained highly independent during the Yayoi and early Kofun periods.
During an investigation of the kouenbu (後円部), the rounded rear of the tomb’s keyhole shape, the remains of a dirt embankment were discovered.
Measuring only 0.35 meters in height, it is nothing more than a path through the rice fields that populate the area. When the tomb was first constructed, however, it was most likely much taller. Judging from the distance from the tomb to the embankment, the moat is estimated to have been around 20 meters wide.
Until this definitive find, debate over its existence had troubled archaeologists for the past fifty years.