Kofun Period (ca. 3rd century–538) Helmet, 5th century; Kofun period Iron, covered with copper-gilt, Japan, The Metropolitan Museum of Art The Kofun period is named after the tomb mounds that were built for members of the ruling class during this time. The practice of building sepulchral mounds and burying treasures with the dead was transmitted to Japan from the Asian continent about the thi..