What is "onbashira"

The is a festival held every six years in the Lake Suwa area of Nagano Prefecture, Japan. The purpose of the festival is to symbolically renew the four shrine buildings at the Suwa Grand Shrine by felling sixteen fir trees, preparing them as honored pillars (onbashira), and transporting them down a mountain to the shrine, where they are erected at the four corners of each building. Festival participants ride the onbashira as they are slid down the mountain, dragged to the shrine, and raised, and the festival has the reputation of being the most dangerous in Japan due to the number of people regularly injured or killed while riding the logs.

The Onbashira festival is reputed to have continued uninterrupted for 1200 years. It is held once every six years, in the years of the Monkey and the Tiger in the Chinese zodiac; however, some sources state that the festival occurs every seven years, because of the traditional Japanese custom of counting time intervals inclusively. Onbashira lasts several months, and consists of two segments, Yamadashi and Satobiki. Yamadashi traditionally takes place in April, and Satobiki takes place in May.