There are about 30,000 keyhole-shaped tombs or kofun (of which around 5,000 can still be visited) have been discovered over a vast area from Kyushu to Honshu. The larger ones (over 200m) are concentrated in the Kinki region – where the center of the ancient state of Yamato emerged.
OZlab: Map of kofun larger than 100 meters in Japan
On the continent, 13 keyhole-shaped tombs dated to the latter half of 5th century to the first half of 6th century – have been found in Korea, all located in South Cholla province in the area of the Yongsan River basin — six of these have been excavated. All 13 tombs were surrounded by moats with many Korean-made “haniwa” (埴輪)-like cylindrical potteries placed on top of these mounds. The tombs also had corridor-style stone chambers, some of which with walls that are painted with red coloring…closely resembling corridor-style tombs in North Kyushu dating to the 5th and the 6th century.
The contents of the tombs had assorted origins – potteries from South Cholla province as well as Kaya and Japan; prestige goods (especially gilt-bronze ornaments) of Paekche origin.
The keyhole-shaped tombs have long been regarded a characteristic unique to Japan during the Kofun period. However, after Dr Kang in-gu’s claim in 1985 that he had discovered keyhole-shaped tomb in the Korean peninsula at the tomb of Changgo-bong — many historians began to claim that the keyhole shaped tombs originated in Korea … like so many of the other continental imports from the Yayoi through the Kofun periods. One popular Korean theory that has been gaining ground claims that the keyhole tombs in South Cholla were constructed for the ruling elites from Paekche who had invaded the Kinki region of Japan to form the dominant ruling group of Kofun period Japan.
Did keyhole tombs originate from Korea?
Archaeological evidence suggests that it is unlikely that Japanese keyhole shaped tombs originated in Korea’s South Cholla, for these reasons:
1) The South Cholla tombs were built from the latter half of the 5th century to the first half of the 6th century, but keyhole shaped kofun mounds were first constructed first in the the second half of the 3rd century in the Kinai region (Nara and the vicinity) then spreading to other parts of Japan, with the tombs reaching massive sizes in the 4th century and into the 5th century. Since the keyhole tombs emerged much later than the largest of the keyhole tombs in Japan, it is hard to hold that keyhole tombs emerged in Korea spreading to Japan.
2) In Japan, mound tombs had already existed from the Late Yayoi period or earlier with many reaching massive sizes in the transition period into the Kofun period, and the evolution of and merging of various shapes into the keyhole shapes over time can be evinced from the layout of the regional tombs. Most Japanese and Western archaeologists and historians believe that “Yayoi evolved without obvious break directly into the KOFUN culture”. By contrast, in South Cholla, at time when keyhole tombs were constructed, square-shaped mounded tombs were also being constructed at the same time indicating that the keyhole tombs were imported ideas from their neighbours in Japan with whom they long had close trading ties. Another evidence of the local South Cholla culture was that the local elites continued to keep their traditional burial culture of giant jar coffins which was distinct from that of incoming Paekche arrivals and its other neighbours.
3) From archaeological viewpoints, it appears that the keyhole tombs in the South Cholla province of Korea were constructed by the local elite group of a culture that was distinct from Paekche’s – but that had long acted as trading intermediaries with its neighbouring groups — with Kaya, Japan as well as the people from Paekche who had begun to expand their territorial control into South Cholla. Archaeological evidence also showed that integration with Paekche only happened much later — the local elite in South Cholla province only became bureaucrats of Paekche after the mid 6th century, judging from the late emergence of corridor style stone chambers of Nungsan-ri type were constructed in the mound of tomb No.3 at Pogam-ri.
From the foregoing, the new and perhaps the most plausible view is that the local ruling elite groups in South Cholla had imported the Japanese Kofun style of building the keyhole tombs, while furnishing a mixture of grave goods with local-Kaya-and-Japanese potteries and gilt-bronze-ornaments-prestige goods from Paekche. It is like that South Cholla acted as a buffer and intermediary zone, one that enriched all those in the Peninsula through trade and demand for its luxury goods, so much so that the its burial customs and societal traits became so similar to and intertwined with those in the Japanese islands. The consensus among scholars is that there was a brisk trading and maritime network between Korea and Japan. The conditions were favourable for royal lineages and certain occupational clans from Kaya, Silla and Paekche to settle in Japan. Northern Kyushu, stretches of the Inland Sea and post-4th century Nara region became areas where the presence of Korean immigrant settlers were particularly felt. It is likely that through a combination of royal alliances and with ruling elites present in Japan as well as coercive force or military action, the Korean ruling elites helped usher the unification of Kofun Period Japan. The clever weaving of key local and regional legends as well as continental ancestral legends in the first historical chronicles, the Kojiki and Nihon Shoki, appears to mirror this process of a minority ruling power coopting, pacifying as well as allying with regional elites in Japan, while consolidating its centralized authority through the creation of a highly stratified caste-like society.
While it is not denied here that many Korean immigrants (from various parts of Korea) brought their skills, techniques and technologies for gilt-bronze working, ironworking, horse-riding, and sueki-ware, the keyhole-construction style of the Kofun tombs remains uniquely Japanese … at least for now.
“Keyhole-shaped Tombs in the Korean Peninsula” by Hideo Yoshii(Kyoto University), translated by Hyung Il Pai (UC Santa Barbara), UCLA Center for Korean Studies, retrieved 28 May 2004