One of the largest groups of keyhole-shaped tumulus (burial mounds) in Hiroshima Prefecture, designated as a National Historic Site

Mitsujō Kofun, located in Saijo-cho, Higashihiroshima City, Hiroshima Prefecture, is a group of ancient tumuli consisting of keyhole-shaped and round tumuli. Tumulus No. 1 is a keyhole-shaped tumulus, having one square end and one circular end and a total length of approximately 92 meters, making it the largest in Hiroshima Prefecture. Built in the first half of the 5th century, this ancient tomb is believed to be the burial site of a powerful clan that ruled the Aki region at the time. It has been restored to its original state and has been open to the public since 1994.

Currently known as Mitsujō Park, it is a popular spot where visitors can experience history up close. Various burial items and haniwa figurines that have been excavated from the burial mounds are on display at the Guidance Corner of the Higashihiroshima City Central Library, located to the east. There is also an exhibition room inside the park management building where visitors can learn about history through explanatory panels about the ancient burial mounds and replicas of haniwa figurines.