Akasaka Tennōzan Kofun

The Tennōzan Kofun is a hōfun (方墳), a rectangular tumulus, at the tip of a ridge extending northwest of Mount Tonomine, near the left bank of the Oubara River. The mound is built in three tiers and is rhomboidal in shape: the northern side is approximately 50.5 meters, the southern side 43.2 meters, the eastern side 46.5 meters and the western side about 47 meters. The top is a flat area about 10 meters on each side. The slopes of each step are covered with fukiishi roofing stones, but no haniwa have been found.

The burial chamber consists of a passageway and an antechamber, with a stone sarcophagus placed in the center of the antechamber, slightly toward the back wall. It is built of natural granite, with corbels visible on the walls. The floor is paved with gravel, and a blocking stone remains at the entrance to the passage. The total length is over 15.3 meters, and the chamber is about 3 to 3.2 meters wide and over 4.2 meters high. The back wall is made of a megalith over two meters high and two more megaliths about one meter high, stacked in three tiers. The left and right walls are also stacked in three tiers, with pebbles placed in the gaps.

The sarcophagus is about 2.4 meters long, 1.7 meters wide and 1.1 meters high. Its lid, made of tuff from Mount Nijō, is shaped like a house, with rope protrusions on the front, back, left and right. The body is a hollowed-out box with a square carving with sides of 48 centimeters from the lid to the body, slightly left of center, and a small window. A small square hole drilled in the upper edge of the body facing the passage was possibly made by grave robbers in antiquity.

The tumulus has been surveyed but has not been excavated, and there do not appear to be any surviving grave goods. The burial chamber structure and the style of the stone coffin suggest that the tumulus was built between the end of the 6th century and the beginning of the 7th century.