It is said that the inner sanctuary of the Grand Shrine of Izumo was once very large. It was 32jo high (about 97m) in ancient times. In the Heian era it was 16jo (about 48m) high, which is larger than the 15jo (1jo = approx. 3.03m) of the Todaji Temple of the Great Buddha, Japan’s oldest great shrine. The present inner sanctuary was built in 1744 and is 8jo (about 24m) high. Other areas pay respect to the great shine and no one is supposed to build another shrine that is 24m high or that surpasses it.
The great shrine is said to have been built in the spot where the god Ookuninushi presented the country he built to the Sun Goddess Amaterasu. The text of the two oldest chronicles of Japan, the Kojiki and the Nihon Shoki both describe a shrine: the Amenomiaraka Shrine in the Kojiki and the Amenohisunomiya Shrine in the Nihon Shoki. They are supposed to be the original Grand Shrine of Izumo. The Grand Shrine of Izumo was called the Grand Shrine of Kitsuki for a long time until its name was changed in the Meiji era.
Though the height of the present building of the Shinto shrine is eight jo (24metres), which corresponds to a building seven stories high, in the Heian period it was twice as high as the present one. This shrine was perhaps the largest wooden building in the world and it was the oldest Taishazukuri (the main Shinto shrine architectural style typified by he Grand shrine of Izumo) structure. The “Kuchizusami”(humming), a textbook for aristocratic children in the mid-Heian period, wrote ‘Unta, Wani and Kyosan’ which is said to show the size ranking of the building at that time. The Grand Shrine of Izumo took the first place, the second one was the Todaiji Temple of the Great Buddha and the third one was the Heian-gu Daigokuden (the council hall of the Heian shrine). At that time, its size exceeded the 15 jo (45 metres) height of the Todaiji Temple of the Great Buddha.
However, surviving records show that its large size caused it to collapse 6 or 7 times during a time span of about 200 years from the mid-Heian period to the beginning of the Kamakura period. It was reconstructed every time.
On the basis of the “Kanawano-gozoei-sashizu” documents of the Grand Shrine of Izumo dating from that time and which are transmitted from generation to generation in the Shrine and Senke families, Toshio Fukuyama, a doctor of engineering created a restoration chart and a major construction company assembled a research team. They created a restoration simulation of the mid-Heian inner sanctuary of the Grand Shrine of Izumo by computer. It showed that the building could withstand earthquakes of a magnitude of about three on the Japanese scale and winds of about 30 metres per second.