Yokose Kofun, also known as Yokose Otsukayama Kofun, is an ancient burial mound located in Yokose, Osaki Town, Soo District, Kagoshima Prefecture. It is a keyhole-shaped burial mound, with a rounded rear section and a rectangular front section, and is designated as a National Historic Site of Japan.
It is the second-largest kofun in Kagoshima Prefecture and is believed to have been constructed during the middle of the Kofun period, around the middle to latter half of the 5th century. Its impressive scale and archaeological finds provide important clues about the political and cultural connections of southern Kyushu in ancient times.
The burial mound stands in a rice-growing area in eastern Kagoshima Prefecture, at an elevation of approximately 6 meters above sea level, west of Shibushi Bay.
Its keyhole-shaped mound faces southwest, with the rectangular front section extending in that direction. The mound itself is approximately 137 meters long, making it the second-largest kofun in the prefecture after Tonjin Otsuka Kofun, which measures 154 meters.
Haniwa, or clay figures and cylinders used in ancient burial rituals, have been found outside the mound. These include cylindrical haniwa and shield-shaped haniwa. Yokose Kofun is the southernmost burial mound in Japan known to have been accompanied by haniwa.
A shield-shaped moat surrounds the mound. It measures approximately 12 to 23 meters in width and about 1.5 meters in depth. Including the surrounding moat, the total length of the ancient burial complex was originally described as reaching 160 meters. Additional outer moats have also been identified on the northern side of the rounded rear section and the southern side of the front section.
The burial chamber is a pit-style stone chamber. It is now exposed at the top of the rear mound. Iron objects and other items are said to have been removed from the chamber in the past.
Artifacts associated with Yokose Kofun include Sue ware, pottery of the Kaya tradition from the Korean Peninsula, and Sue ware produced in the Tsuboi area, also known as Suemura in present-day Osaka Prefecture.
Other burial mounds are said to have once formed a group around Yokose Kofun. Some researchers have suggested that these may have served as subsidiary burial mounds associated with the main tomb.
Based on its shape, burial chamber, and excavated objects, Yokose Kofun is believed to have been built between the middle and latter half of the 5th century, during the middle Kofun period.
Within the history of southern Kyushu, it is regarded as a major ruling-class burial mound following the Osahozuka and Mesahozuka tombs in the Saitobaru Kofun Group in Saito City, Miyazaki Prefecture.
As a coastal keyhole-shaped burial mound, Yokose Kofun is considered important evidence of connections between the Yamato court, the southwestern Japanese islands, and the Korean Peninsula. Its structure and artifacts offer insight into the movement of people, goods, and cultural influences across the region during the 5th century.
The area containing Yokose Kofun was designated a National Historic Site of Japan in 1943 (Showa 18).
Other important ancient burial sites are distributed in the surrounding area. These include the Tonjin Kofun Group in Higashikushira Town, which contains Tonjin Otsuka Kofun, and the Jinryo Kofun Group in the Jinryo and Yokose areas of Osaki Town. These burial mounds are thought to have been constructed before Yokose Kofun.
Yokose Kofun has attracted attention for many years. It was already described as “Otsukayama” in historical works such as the Osaki Meishoshi, compiled in 1824 (Bunsei 7), and the Sangoku Meisho Zue, completed in 1843 (Tenpo 14).
Around 1902 (Meiji 35), the tomb was damaged by grave robbing. Later archaeological investigations helped clarify the extent and structure of the burial mound.
Investigations conducted during fiscal years 2010–2011 provided more detailed measurements of the mound and its surrounding moats.
The width of the inner moat varies around the mound. It measures 6 to 8 meters beside the rear section, 12 meters on the western side and 20 meters on the eastern side of the narrow connecting section, and 7 to 11 meters beside the front section.
The outer moat measures approximately 3.5 meters wide beside the rear section and 2.5 meters beside the front section.
Because the burial mound was constructed on sloping ground, the rounded rear section was built approximately 1 meter higher than the front section.
The pit-style stone burial chamber is now exposed at the top of the rear section. However, the original rear mound is believed to have been higher than its present form.
Artifacts excavated from Yokose Kofun are preserved and displayed at several institutions in Kagoshima Prefecture.
Yokose Kofun is an important example of the large burial mounds built in southern Kyushu during the 5th century. Its 137-meter-long keyhole-shaped mound, extensive moats, exposed stone burial chamber, and distinctive pottery finds reveal the sophistication of the region’s ancient burial culture.
The site is particularly significant for understanding relationships between the Yamato court and communities in southern Japan, the southwestern islands, and the Korean Peninsula. Its designation as a National Historic Site and the archaeological investigations carried out over many decades have helped preserve this valuable record of ancient history.