The shrine buildings at Naikū and Gekū, as well as the Uji Bridge, are rebuilt every 20 years as a part of the Shinto belief of the death and renewal of nature and the impermanence of all things and as a way of passing building techniques from one generation to the next. The twenty-year renewal process is called the Shikinen Sengū. Although the goal of Sengū is to get the shrine built within the 20-year period, there have been some instances, especially because of war, where the shrine building process is postponed or delayed. The original physical purpose of the Sengu process is unknown. However, it is believed that it serves to maintain the longevity of the shrine, or possibly as a gesture to the deity enclosed within the shrine. Historically, this cyclical reconstruction has been practiced for many years in various shrines throughout Japan, meaning that it is not a process exclusive to Ise. The entire reconstruction process takes more or less 17 years, with the initial years focusing on project organization and general planning, and the last 8 years focusing on the physical construction of the shrine.