The three Kanto regions

...This pass runs up the valley of Asakawa, a tributary of the Tama River, and crosses Koshu. It is the saddle between Mount Kagenobu (727m) in the north and Mount Takao (600m) in the south. During the Edo period, it was a key point on the Koshu Kaido road that connected Kanto and Koshin, and Kobotoke Pass, located in Komakino at the eastern foot of the pass as a key point on the mountain defense line west of Edo, was called one of the three checkpoints of Kanto along with Hakone and Usui checkpoints. However, in the Meiji period, the Koshu Kaido road was changed to go via Odarumi Pass (389m) at the foot of Mount Takao in the south, so Kobotoke Pass was left behind by the times.

*Some of the terminology used to refer to the "Three Kanto Regions" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…多摩川の支流浅川の谷をのぼって甲州にこえる峠で，北の景信（かげのぶ）山(727m)と南の高尾山(600m)の鞍部にあたる。江戸時代には関東と甲信を結ぶ甲州街道の要所で，江戸の西側山岳防衛線上の要衝として峠の東麓の駒木野におかれた小仏関は，箱根･碓氷両関とともに関東の三関といわれた。しかし，明治に入ると甲州街道は南の高尾山麓大垂水（おおだるみ）峠(389m)経由に変更されたため，小仏峠は時代からとり残された。…

※「関東の三関」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報