In ancient Japan, the size of tombs and attitudes toward death changed as time went on, and this is thought to have been influenced by ancient China. In the Kinki region, "square trench tombs," which were filled with earth and surrounded by ditches, and "mound tombs," which were mounds built of earth, became huge, leading to the development of the kofun tombs. The anterior and posterior round tombs built in this way were the crystallization of advanced civil engineering technology and were unique to Japan.
As culture developed from the Jomon period to the Yayoi period, there was a major change in the way Japanese people looked at tombs. In the Yayoi period, graves became more communal and grouped, and at the same time, huge tombs were built for people of high status.
In the latter half of the 4th century, giant anterior and posterior tombs were constructed. The increasing size of tombs and the view of the afterlife as a spiritual foundation are thought to be evidence of the spread of ancient Chinese values to East Asia. At present, about 4,700 anterior and posterior circle tombs have been confirmed nationwide, from Iwate to Kagoshima prefectures, with the larger ones concentrated in the Kinki region. Kofun tombs are not simply tombs filled with earth, but structures that were built by precisely surveying, measuring, designing, cultivating the land according to the specifications, and preparing the ground.
Let's take a look at the external structure of the anterior and posterior tombs. First of all, the part of the tomb that is heaped high with soil and stones is the "mound," which is the central part of the tomb. In some of the larger tombs, the slope is like a staircase or a stone wall. The stones piled on the surface were round stones or broken stones, which are called thatched stones. Thatched stones seem to have been used to prevent the soil from flowing out. However, thatched stones were only used in the early to mid Kofun period, and will no longer be seen in the late period when the size of the tumulus is shrinking. There is a protruding part called "Zoukei" in the neck where the front part and the back part join. It seems that earthenware and clay figurines were laid out here for rituals. The highest part of the tomb is the "top of the tomb," which contains a stone chamber with a coffin and a burial chamber to cover it, and is the "main part" where the burial mound is placed. There is a drainage channel under the burial chamber, and paint such as mercury vermilion was often applied to the inside and outside of the burial chamber and to the stone chamber for preservation.
The burial mound was surrounded by a waterless shelter, but in the plains it became a moat filled with water for irrigation. The construction of the burial mounds involved not only advanced civil engineering technology, but also water management technology. A large number of workers were needed to complete the huge tombs. It is thought to have taken several decades at most, indicating that there was a chieftain with that much power at the time.
From the latter half of the 4th century, huge burial mounds were built all over the country. This indicates the expansion of the Yamato regime's power, but the reason for this is unclear and is called the "blank 4th century. The largest burial mounds in Japan, the Hyakudzu burial mounds, were built on the coastline of the time, apparently to show the power of the king to foreign envoys.
The anterior and posterior round burial mounds are a unique type of burial mound in Japan. However, in terms of the internal structure, the side-hole stone chamber, which appeared at the beginning of the 5th century and was excavated from the side of the mound, seems to have been created through exchange with Baekje. In the southern part of the Korean Peninsula, more than a dozen anterior and posterior round tombs built in the late 5th to early 6th centuries have been discovered. It has been pointed out that influential Japanese people of the time may have traveled to the area, or that they may have imitated forces from the region.
The Momozu Tumulus Group in Osaka Prefecture is a World Heritage site. Three of the tombs have been designated as emperor's mausoleums, two as mausoleum reference sites, and 18 as mausoleum jidotokos by the Imperial Household Agency. The largest tomb is the Daisenryo Tumulus (the tomb of Emperor Nintoku), which is the largest tomb in the world in terms of surface area, surpassing the Khufu Pyramid and the Mausoleum of the First Emperor.