Oyama Yoshimasa

Shugo of Shimotsuke Province

Oyama Yoshimasa was a fourteenth-century warrior lord and head of the Oyama clan, a line that had held the post of military governor (shugo) of Shimotsuke Province since the Kamakura period and dominated the area of today's city of Oyama, in Tochigi Prefecture. His name is closely tied to the revolt he waged from 1380 to 1383 against Ashikaga Ujimitsu, Kamakura kubō and representative of the Ashikaga shogunate in the Kantō. During this conflict he relied on the clan's fortified strongholds, chiefly Washi Castle, together with Gion Castle and, probably, Nakakuki Castle, which is identified with the Iwatsubo of the chronicles. Besieged and ultimately cornered, he took his own life; his defeat led to the eclipse of the clan's main branch, whose name was later revived by a branch descended from the Yūki. The castles associated with this episode are today protected as a National Historic Site.