The tumulus is surrounded with empty moats in about 20 meters depth, which is seen as the outer moat, was confirmed on the south side of the front square part by the results of the research.
古墳の周囲には空濠がめぐるが、発掘調査の結果、前方部の南側に幅約20メートル深さの溝が確認されており、外濠とみられている。