Mystery No.7 How to construct kofun?

Construction of kofun required unimaginably hard work. For example, it is estimated that it would have taken 15 years and 8 months to construct Nintoku-tenno-ryo Kofun, even if a maximum of 2,000 people per day were engaged. Therefore, it can be said that only those who had a large labor force and plenty of materials could have built kofun.
In order to construct kofun, it was necessary to find a suitable location, mow a field, and level the land. Then, according to the design, ground was dug along the outline of planned mound, and earth was heaped up. Excavated areas became a moat and the mound was often made in a few tiers. At some kofun like Guwashobo, earth mounded like fish scales was found. Possibly this was to reinforce the mound. After completion of the mound, fukiishi paving stones and haniwa figures were placed, and then, a burial facility was made. Once the dead was buried, a stone chamber was sealed up. This is the whole procedure. At Nisanzai Kofun, a wooden bridge, which must have been built just before or after its completion, was found. It might have been used for funeral rites including carrying the coffin to the mound.

Set of yellow and brown soil piled up.