The Mihashira or Onbashira (Japanese: 御柱, honorific prefix 御 on-/mi- + 柱 hashira 'pillar') are four wooden posts or pillars that stand on the four corners of local shrines in the Lake Suwa area of Nagano Prefecture (historical Shinano Province), Japan.

[3][4][5][6] The shrine's deity, known either as Suwa Daimyōjin or Takeminakata, was worshipped since antiquity as a god of wind and water,[7] as well as a patron of hunting and warfare.

[14] This was later joined by two Buddhist structures (no longer extant since the Meiji period): a stone pagoda in the shrine's inner sanctum known as the Tettō (鉄塔), 'iron tower', and a sanctuary to the bodhisattva Samantabhadra (Fugen)—Suwa Daimyōjin being considered to be a manifestation of this bodhisattva—on the sacred mountain.

[10][16] Unlike today, there were originally far fewer buildings in the precincts: in the Kamisha Honmiya's case, medieval records for instance indicate that the shrine's most sacred area where a worship hall (haiden) now stands once featured only a torii gate and the god's dwelling place, the iwakura, demarcated by a kind of fence (kakusu (格子)).

[20][21] The actual thickness of the logs used may vary: the largest onbashira in recent history in terms of girth is the Akimiya's ichi no hashira used in the festival of 1950 (Shōwa 25).

[24] Some scholars meanwhile consider the practice of erecting sacred pillars to derive ultimately from prehistoric tree worship, citing the remains of wooden poles or slabs discovered in various Jōmon period sites in apparently ritualistic contexts as potential parallels to the Suwa onbashira.

For instance, the ritual roughly reflects the elements' cycle of generation (wood begets fire, fire begets earth, earth begets metal), in that the Upper Shrine's onbashira are made out of trees from a mountain to the east (associated with the element of wood) and are brought to the shrine, located south (fire) of Lake Suwa (north, water) in order to replace old onbashira (earth), which are taken down and brought to Hachiryū Shrine in the former village of Chū-kaneko (中金子, with 金 meaning metal), now a part of Suwa City.

[32] The timing of the Onbashira Festival, which falls during the Zodiac years of the Tiger and the Monkey, and the rebuilding of the Upper Shrine's hōden or treasure halls (see below) at noon—the hour of the Horse—are seen as corresponding with the concept of the Three Unities (三合, Chinese: Sānhé, Japanese: Sangō),[33] where four of the five elements are assigned three branch signs each, representing 'birth' (長生), 'peak' (帝旺), and 'burial' (墓).

[39][27][28] One legend concerning Suwa Daimyōjin claims that he appeared to the general Sakanoue no Tamuramaro, appointed by Emperor Kanmu to subjugate the indigenous Emishi of northeastern Japan.

[8][40][41][42] In thanksgiving for the god's miraculous assistance in Tamuramaro's campaign, the imperial court was said to have decreed the establishment of the various religious ceremonies of Suwa Shrine.

[39] The Ekotoba describes the preparations for the rebuilding thus: at the onset of spring, the governor (kokushi) of Shinano would appoint officials who collected the necessary funds from the populace from checkpoints or toll booths (seki (関)) set up in provincial roads in exchange for mifu (御符), official certifications stamped with the sacred seals of the Upper and Lower Shrines.

[46] Due to the exorbitant amount of money required for the project, locals traditionally avoided or postponed special occasions like marriages, coming-of-age ceremonies, or even funerals during the year.

[47][48] In addition, observance of the event in the proper time was considered essential: failure to obey these taboos was thought to incur divine punishment.

Indeed, the shrine's ceremonies would have been lost to oblivion had not the warlord Takeda Shingen, a staunch devotee of the Suwa deity, took steps to revive their performance.

[50] In 1565, after he had fully conquered the whole of Shinano Province, Shingen issued an order for the reinstitution of the religious rites of both the Kamisha and the Shimosha, the zōei being one of them.

[51][52] In 1582 (Tenshō 10), the eldest son of Oda Nobunaga, Nobutada, led an army into Takeda-controlled Shinano and burned the Upper Shrine of Suwa to the ground.

As the union between Shinto and Buddhism that existed then at the shrines—as in most places in Japan—was brought to an end[59] and control over the Upper and Lower Shrines (merged into a single institution in 1871) was turned over from local priestly families to the government, the Onbashira Festival itself underwent massive changes.

[61][62] The Lower Shrine's iconic Kiotoshi, wherein the onbashira are slid down a steep hill (the Kiotoshi-zaka) as men attempt to ride it, originated from the Meiji period onwards.

[66] During the final years of World War II, as Japan's military situation became more desperate, the government began altering its original conscription laws, so that in 1943, all male students over the age of 20 became subject to the draft, whereas they had formerly been exempted.

[76] In 2010, two men, Noritoshi Masuzawa, 45, and Kazuya Hirata, 33, died after falling from a height of 10 metres (33 ft) as a tree trunk was being raised on the grounds of the Suwa Grand Shrine.