Every twenty years, the gods move house.

It is not only the buildings that are renewed. The fences and gates around the sanctuary, the treasure houses, and the 1,576 sacred objects in 714 categories known as Goshōzoku Shinpō — swords, bows and arrows, mirrors, textiles, even brushes and inkstones — are all made anew in the ancient manner. Besides the two main shrines, the 14 auxiliary shrines (betsugū) are rebuilt in turn.

Each sanctuary has two sites of equal size, east and west. While the buildings stand on one, the other waits as a bare plot covered in white pebbles, the kodenchi. In the middle of the kodenchi stands a tiny hut. Beneath it is the spot where the shin-no-mihashira, a sacred pillar set under the centre of the sanctuary floor, stood — carefully guarded until the next rebuilding.

The Sengu is not just the day the deity moves into the finished sanctuary. Taking the 62nd (2013) as an example, it was eight years from the first rite to the transfer, with more than 30 ceremonies and events carried out in a fixed order.

One Sengu needs roughly 10,000 hinoki cypress trees. The largest pillars require giants over a metre in diameter and more than 200 years old. In ancient times, the timber came from Mt. Kamiji and Mt. Shimaji behind the shrine — the misomayama, or sacred timber mountains. But as the rebuilding was repeated, good trees ran out. From the Kamakura period the source moved to Mikawa and Mino, and from the mid-Edo period to the mountains of Kiso.

Alarmed, Jingu drew up a forest management plan in 1923. The goal: in 200 years, to supply the timber once again from its own forest. This ultra-long-term plan, which began with planting, is bearing fruit. For the 62nd Sengu in 2013, cypress grown in the shrine forest was used for part of the timber for the first time in about 700 years.

In the late Muromachi period, around the Ōnin War, the finances of both the imperial court and the shogunate collapsed, and no one could pay for the Sengu. Naikū's last rebuilding was in 1462, and Gekū's had stopped even earlier; for both shrines the gap exceeded 120 years. The buildings decayed, and rites were carried on in temporary halls.

The person who changed this was Seijun, a nun of Keikōin, a Buddhist convent in Uji. She travelled the provinces collecting donations (kanjin), first rebuilt Uji Bridge, and in 1563 finally achieved the Gekū Sengu — the first in 129 years. Her successor Shūyō secured the backing of Oda Nobunaga and Toyotomi Hideyoshi, and in 1585 both shrines were rebuilt in the same year. Throughout the Edo period, Keikōin remained deeply involved in the practical work of the Sengu.

Butterfly effect: what one interruption created

1. 1467–Ōnin War and bankruptcyThe court and shogunate can no longer fund the Sengu
2. 15–16cSengu stops; fundraising beginsNuns of Keikōin collect donations from commoners across the provinces
3. 16c–Ise becomes the people's shrineFor those who gave, Ise became "our Jingu"
4. 17c–Oshi networks spread nationwideIse-kō associations form everywhere; pilgrimage becomes a popular dream
5. 1705–Okage Mairi of millionsSometimes called Japan's first mass-tourism boom

The parts of the old sanctuaries are not discarded. The most famous example is the fate of the munamochi-bashira, the thick free-standing pillars at each end of the sanctuary that support the ridge.

Naikū's old ridge pillars are reshaped into the inner torii of Uji Bridge (on the shrine side) and Gekū's into the outer one. Twenty years later, the Uji Bridge torii are raised again at the Higashi-no-Oiwake in Seki-juku, at the foot of the Suzuka Pass on the Tōkaidō, and at the Shichiri-no-Watashi ferry landing in Kuwana. In the Edo period, travellers from the east passed under the torii at Seki, and those arriving by boat under the one at Kuwana, and felt they had entered the province of Ise.

Other old timber goes to shrines across Japan for repairs and rebuilding. After the Great East Japan Earthquake of 2011, Jingu's old timber was used to rebuild damaged shrines.