Tenshu

Tenshu (天守, 天主, 殿主, 殿守, also called tenshukaku, 天守閣) is an architectural typology found in Japanese castle complexes.

Tenshu are characterized as typically timber-framed, having multiple stories, being seated on ishigaki (dry stone) foundations, and having individual floors delineated by surrounding tiled eaves.

Further, tenshu are typically decorated with varying patterns of dormer gables (chidori-hafu), and are capped with hip-and-gabled roofs (irimoya-hafu) with shachihoko finials.

The first known use of the term tenshu can be found in Yoshida Kanemi's journal, Kanemi kyōki, in the entry for the 24th day, 12th month of Genki 3 (27 January 1573): 明智為見廻下向坂本…城中天主作事以下悉披見也、驚目了… Left the capital with Akechi [Mitsuhide] for Sakamoto for the purpose of a survey...in the center of [Sakamoto] castle, all saw that a tenshu (天主) was being built and were surprised…[1]Subsequent mentions in Kanemi kyōki and in other primary sources (such as Tennoji-ya kaki, Tamonin nikki, and in the letters of both Oda Nobunaga and Toyotomi Hideyoshi) during the 1570s reveal two points about the emergence of the term.

Most Edo period castles were built during a period of peace lasting more than two centuries, but legends about earlier warfare suggested that once the outer defences of a castle had been breached, the defenders generally preferred to set fire to the remaining buildings and sally out to their deaths, rather than fight it out inside a fragile tenshu.

Hundreds of them were destroyed or dismantled during the final stages of the unification wars of the Sengoku period at the turn of the 17th century.