The Shikinen Sengū Interval

Issue 278 of Shintō Shūkyō included an interesting article speculating on the reasons why the Shikinen Sengū at Isë Jingū is held every twenty years: “The Foundations for Determining the Year for Transfer of a Deity (Sengūshiki): Sakutan usui and the Regulations for Official Storehouses”, by Ōno Yoshiyuki.

The Shikinen Sengū is held every twenty years. Today, that means that the last one was in 2013, and the next will be in 2033. Originally, however, the year in which it was held was year one, and it was held again when that count reached twenty — so nineteen years later. There are many theories about the reason for this interval, none of which are universally accepted. Ōno rejects one — the idea that the interval ensures that necessary craft techniques will be passed from one generation to the next — on the grounds that all the techniques were in common use across Japan when the ceremony started. This is an important factor now, but it could not have been the reason for setting the interval in the first place.

I am going to reverse the order of his article, and start with the rice storage issue. The contemporary regulations for the state say that the longest-lasting form of rice can be stored for twenty years. Ōno argues that this must have been based on actual durability, because this rice was an important part of the national budget, and the numbers and rice categories are different from the Chinese law codes on which the Japanese one was modelled. This rice was also saved up to pay for the Shikinen Sengū. Thus, he suggests, the reason for the interval being roughly twenty years was that this was the longest period they could save up.

That then raises the question of why the nineteen year cycle was chosen. A lot of people have noted that this is the cycle over which the lunar and solar calendars come back into synchronisation. For example, if the winter solstice is a full moon this year, it will be a full moon again in nineteen years — roughly. Ōno explains that, because of the way ancient calendars were calculated, there was one day in the year, the base, for which this was not rough. The calculations ensured that this day would fall on the first of a month every nineteen years.

The first Shikinen Sengū was ordered by Tenmu Tennō, but then he died, and it seems to have been cancelled. It was reordered by Jitō Tennō, his wife and successor, and happened two years after her order. Originally, the preparations seem to have taken only two years, and the Inner Sanctuary was done first, followed by the Outer Sanctuary two years later. (The ceremony seems to have been smaller originally, and Ōno suggests that budgetary constraints may have made it hard to start earlier.)

If we look at the years, and assume that Tenmu Tennō intended the ceremony to happen two years after his order, that ceremony would have happened in the year in which the base for the calendar fell on the first of the month, and thus all future Shikinen Sengū would also have done so. Between the two Tennō, the calendar was changed, and the year in which the first Shikinen Sengū took place was the year in which the new calendar’s base fell on the first of the month.

Obviously, if this was the original intent, it went completely out of the window later on, possibly because people had forgotten. The evidence here is not overwhelming, but I do think that this is a plausible theory of the reason for both the interval, and the choice of starting year. And that is all the Ōno claims for it.