Oyama

The Oyama were a provincial gōzoku house of Shimotsuke, claiming descent from the tenth-century warrior Fujiwara no Hidesato through the Ōta family. Around 1150 Oyama Masamitsu settled at Oyama Manor and took its name; his wife was the wet nurse of Minamoto no Yoritomo. His son Tomomasa fought in the Ōshū campaign of 1189 and became shugo governor of Shimotsuke and Harima.

Ranked among the great Kantō houses, the Oyama suffered disasters. In the Genkō War of 1333 Sadatomo was killed, and his successor Hidetomo switched to Nitta Yoshisada's army in the attack on Kamakura. A later rising by Oyama Yoshimasa was crushed by Ashikaga Ujimitsu, and the name continued through an adopted heir from the Yūki.

During the Sengoku wars the Later Hōjō overran Gion Castle in 1576, ending the Oyama as territorial lords. Their descendants later served the Mito Tokugawa as retainers.