The Azuma Kofun is located on a narrow plateau between the Ogawa and Sugata rivers, which run north and south through the northern Kantō Plain. As a result of an archaeological excavation from 2007 to 2010, it was determined that the tumulus is a built in two tiers. The lower tier (base) is wide, and with a total length of about 128 meters was found to be the largest in the prefecture. The second tier is about 86 meters long with a height of about 10 meters. The two-tiered mound is set on a base of similar shape, and is surrounded by a moat with a width of about 20 meters and a depth of about three meters. Pumice deposits from the 1108 AD eruption of Mount Asama were confirmed from the soil filling the moat. The burial facility is a horizontal hole type stone chamber with dimensions of 2.4 meters long x 1.7 meters wide x 2.0 meters high; however, during the Edo period, the front part of the rectangular portion of the tumulus was destroyed, and the entrance stone and one of the ceiling stones were removed by the daimyō of Mibu Domain for use as ornamental stones in the gardens of Mibu Castle, where they can still be seen. The entrance stone was of cut tuff with a rectangular opening for a door, whereas the ceiling stone (and remaining stones in the walls and remaining ceiling of the burial chamber) are of monolithic diorite. Red pigment was applied to the walls of the burial chamber, which was backfilled for preservation after the 2010 excavation.