Chigi (a roof material) and Katsuogi (a roof material) (千木・鰹木)

Chigi/katsuogi is a material provided on roofs of buildings, but nowadays is found only in shrine buildings.

Chigi indicates crossed trees placed at each end of a roof, and katsuogi is a number of trees placed in parallel with each other but perpendicularly to the ridge of a roof. Originally, both of them were used in the residences of persons of the upper class. However, they are nowadays seen only in shrines and have become symbolic with shrine buildings.

In ancient times, two wooden logs were simply crossed and tied together to make a roof without their tips being cut neatly. Chigi is considered to reflect such past practice. It is considered that both chigi and katsuogi were to reinforce the structure. It is said that the term katsuogi originates from its shape which resembles a dried bonito.
Katsuogi (鰹木) is also written as '堅緒木,' '堅魚木,' '勝男木' or '葛尾木.'

In shrines in the Izumo area including Izumo Taisha Shrine, the sotosogi style (both ends of chigi are cut vertically) is used for the shrines whose god is male and the uchisogi style (both ends of chigi are cut horizontally) for the shrines whose god is female. The other shrines follow these styles. It is also considered that for the number of katsuogi, an odd number is yang and an even number is yin. Therefore, an odd number of katsuogi was used for male-god shrines and an even number for female-god shrines.

However, at Ise-jingu shrine, the main god of Kotai-jingu Shrine and Toyouke Dai-jingu Shrine are female, Amaterasu Omikami and Toyoukebime, respectively, but the chigi is cut in the uchisogi style and the number of katsuogi is ten for the inner shrine, and the chigi is cut in the sotosogi style and the number of katsuogi is nine for the outer shrine. Similar situations are also found in the betsugu (shrines built separately from the main shrine) as follows. For example, Tsukiyomi no miya (literally, "moon-reading palace"), which is a betsugu in the inner shrine, and Tsukiyomi no miya (literally, "moon night-viewing palace"), which is a betsugu in the outer shrine, are dedicated to the same male god whose name is Tsukuyomi (written Tsukuyomi no mikoto at the betsugu in the outer shrine, literally, "moon night-viewing male god"). However, regardless of whether the main god is male or female, betsugu in the inner shrine have uchisogi-style chigi and an even number of katsuogi, whereas betsugu in the outer shrine have sotosogi-style chigi and an odd number of katsuogi. The same rule applies to Sessha (shrines where gods related to the gods in the main shrine are worshiped), Massha (small shrines belonging to the main shrine) and Shokansha (shrines where the gods of clothing, food and housing are worshiped). There are various theories regarding an explanation for this rule, but it has been speculated that the main god in the outer shrine may originally not have had masculine properties.