Artifacts uncovered include cylindrical and "morning glory-shaped" haniwa, Haji ware, and Sue ware pottery, from which the tumulus is estimated to have been built in the latter half of the 6th century AD.

Another unusual feature is a protrusion extending from the western side of the tumulus, near the joint between the rectangular and circular portions.

From the results of ground-penetrating radar surveys and excavation on the posterior circular portion of the tumulus, it is known that there is a horizontal-type stone burial chamber that is orientated to the south.

The name "Teppōyama" comes from the fact that tumulus was used as a gunnery training center of Oshi Domain during the Edo period.

The training ground was located near the northern constriction, and the mound was modified to form the backstop behind targets used in rifle practice with an embankment constructed to shelter the person near the targets who confirmed whether or not the shooter's aim was correct.