Koyasan is the name of an area located in Koya-cho, Ito-gun, northern Wakayama Prefecture. The town spreads across a mountain basin at an altitude of about 800m, surrounded by mountains of around 1,000m. Although it is called "Koya-san" (Mount Koya), it is not a mountain in the geographical sense. Within Koyasan, the entire area is considered temple grounds, known as "Ichizan Keidaichi," and it is a town that developed within the temple grounds. Originally, Koyasan as a whole and Kongobu-ji Temple were synonymous. The Koyasan Shingon sect has Kongobu-ji Temple in Wakayama Prefecture as its head temple, the Okunoin of Koyasan and the mausoleum of Kobo Daishi as the source of faith, and the Danjo Garan as a training hall, conveying the teachings and traditions of Shingon Esoteric Buddhism to this day. Koyasan was founded in 816 AD by Kobo Daishi Kukai, who received an imperial decree from Emperor Saga to establish Koyasan as the fundamental training ground for Shingon Esoteric Buddhism. Kongobu-ji Temple, the head temple, is said to have been named from the scripture "Kongobō Rōkaku Issai Yoga Yugi-kyō," meaning "this mountain is the most supreme and most revered peak that must be protected forever."