All the large keyhole-shaped tomb mounds found in the Korean Peninsula were built in a very limited period of time between the late fifth century and mid sixth century, only in the area that used to be the westernmost part of Gaya's sphere of influence before Baekje moved to the south, and they are known for containing Japanese relics, such as ento haniwa (cylindrical haniwa), shell products made in south islands, and an rock chamber painted with bengara (iron oxide red pigment).
また朝鮮半島の前方後円墳はいずれも5世紀後半から6世紀中葉という極めて限られた時期に成立したもので、百済が南遷する前は伽耶の勢力圏の最西部であった地域のみに存在し、円筒埴輪や南島産貝製品、内部をベンガラで塗った石室といった倭系遺物を伴うことが知られている。