Tomomasa Oyama

A military commander in Shimotsuke (Tochigi Prefecture) from the Heian to Kamakura periods. Shugo of Shimotsuke and Harima (Hyogo Prefecture). Son of Masamitsu. Called Koshiro, he held the ranks of Uhyoe-no-jo, Saemon-no-jo, Kebiishi, Shimotsuke no Kami, and Junior Fifth Rank. In 1183 (Juei 2), he distinguished himself in the Battle of Noginomiya, and was appointed land steward of Murata Shimosho in Hitachi Province (Ibaraki Prefecture) and Hyuga-no-go in Shimotsuke Province. He played an active role as a powerful vassal during the founding period of the Kamakura Shogunate. In 89 (Bun'i 5), he participated in Minamoto no Yoritomo's conquest of Oshu, and in 90 (Kenkyu 1), he accompanied Yoritomo to Kyoto and was appointed Uemon-no-jo. In 1201 (Kennin 1), he went to Kyoto and served as a guard. During the Jokyu War (1221), he remained in Kamakura as one of the senior retainers. Around 1226 (Karoku 2), he became a monk. His posthumous name was Seisai. He died on March 30, 1264, at the age of 84.

[Takashi Shinkawa]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

平安～鎌倉時代の下野(しもつけ)（栃木県）の武将。下野、播磨(はりま)（兵庫県）の守護。政光(まさみつ)の子。小四郎(こしろう)と称し、右兵衛尉(うひょうえのじょう)、左右衛門尉、検非違使(けびいし)、下野守(しもつけのかみ)、従(じゅ)五位下。1183年（寿永2）野木宮(のぎのみや)合戦で功をたて、常陸(ひたち)国（茨城県）村田下荘、下野国日向野(ひがの)郷の地頭職に補任(ぶにん)された。鎌倉幕府創業期の有力御家人(ごけにん)として活躍。89年（文治5）源頼朝(よりとも)の奥州征伐に参陣し、90年（建久1）頼朝上洛(じょうらく)に供奉(ぐぶ)し、右衛門尉に任官した。また1201年（建仁1）上京して大番役を務めた。承久(じょうきゅう)の乱（1221）には宿老の一人として鎌倉にとどまった。26年（嘉禄2）ごろ出家。法名生西。嘉禎(かてい)4年3月30日没。84歳。

［新川武紀］

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