In 1998, a national record of 33 Sankakubuchi Shinjukyo Mirror (a round mirror with raised edge and relief engraving of animals and gods) along with one Gabuntai Shinjukyo Mirror (a mirror with figures of deities and sacred animals), numerous iron swords, and U-shaped iron products were excavated from Kurozuka Tumulus, a keyhole-shaped mound built in the beginning of the Kofun period (tumulus period).
古墳時代初期の前方後円墳である黒塚古墳から1998年に国内最多の三角縁神獣鏡33面、画文帯神獣鏡1面、大量の鉄製刀剣類、U字形の鉄製品などが出土した。