The Torii mark the boundary between the material outside world and the sacred space of the shrine and have become a particularly iconic symbol of Japanese religion.
Torii - Gateways to the Sacred
Torii, the iconically Japanese gateways that typically mark the entrance to Shinto shrines are ubiquitous all over the country, and are even used as a symbol on maps to mark the location of a shrine.
Buddhist temple locations will be marked with a swastika. Torii range in size from only a few inches high to monumental structures straddling roads such as the massive torii on the road to Heian Shrine in Kyoto, and while wood and stone were the earliest known construction materials, concrete, steel, bronze, ceramic, and even plastic is used sometimes.
Origin of Torii
As with many Japanese traditions the exact origin of torii is not known and there are mainly two competing theories, one saying that it is an indigenous invention, and the other that it is a variation on an imported idea.
Neighboring cultures with symbolic gates that may have influenced the design of torii are the Hongsal-mun of Korea, the Pailou of China, and the Torana of India, with the latter being a strong contender as some sources say that the legendary monk Kukai introduced a torana in the ninth century. As the first mention of torii in any texts is not until the tenth century, credibility is added to this particular theory.
Torii were probably not just associated with shrines, but rather many kinds of sacred space, however in the early years of the Meiji Restoration (1868-) the government banned the use of torii at any place other than officially registered shrines of the new State Shinto, which is why even today certain of the Sect Shintos still do not use a torii. Nowadays, however, torii can be seen in Buddhist temples at the entrance to the temple's own shrine or chinjusha.
Torii, lit. "bird perch" marks the transition from the profane to the sacred and may sometimes be hung with shimenawa or a sacred rope festooned with zig-zag-shaped folded pieces of white paper.
There are a wide variety of torii styles with numerous sub-styles, as well as individually unique torii. The most commonly seen style is known as Myojin Torii. These feature an upwardly curving top lintel, known as kasagi, and a common sub-style is Ryobu that feature a pair of small pillars supporting the main pillars.
Another major style is Shinmei, featuring uprights, hashira, and cross pieces that are straight. Torii of this style became very popular with the rise of state Shinto because of their link to Imperial sites.
One other type of small torii needs mentioning. Driving in the countryside you may see small vermillion torii by the side of the road. Sometimes they may actually be marking a small altar, but many times they are simply a warning not to dump trash.
Iconic Torii in Japan
The torii found at some shrines have become iconic images of Japan. One example is the torii of Itsukushima Shrine, located on the shore of Miyajima island, in Hiroshima. Traditionally, travelers had to go under this torii before setting foot on the sacred land of the island. It's also one of the "three views of Japan". Another example are the torii tunnels of Fushimi Inari-taisha, a shrine dedicated to the Inari deity. Here several thousand torii are lined up to create tunnels on the paths up the hill where the shrine is located.