Torii is the facility which shows the boundary of gods area, but it is unknown the origin yet.
This famous big Torii is the Myojin Torii style, but it has the round table on the top of pillars, thus, it is called Inaritorii or Dairintorii.
The first record which mentioned about this Torii is Wakasagunkenshi and it is written that it was made in Ouei 2(1395), but it is also written that it was re-built after the collapsed big Torii. Thus, it should have been exist before. Two records of re-building the Torii were found since then and the last record is in Syusuizatsuwa and it mentions the re-building in Genroku 7(1694).
It is a wooden Torii, about 6.4m in height. The distance between the pillars is 4.63m. The diameter of the pillar is 48.25cm. Copper plate is put on top and same as the frame in centre. The reinforcement work has been also done for important parts.
It is said that the pillar was made with Yashiromatsu(black pine tree), but it was found that it is Himuro tree, according to the recent investigation. It can also be called Yashiromatsu as same words, thus, there might be a mistake. Because of the typhoon in Meiji 42(1907), it was collapsed once. Thus, to keep these holy pillars, the bottom parts of the pillar became stones.
It is a well-balanced Torii, even 300 years passed.
Explanation 
Hachiman shrine
