For early Tenshu, functions primarily as living quarters were considered important and some Tenshu were not constructed on the foundation in Kuruwa (castle compound), such as the four-story structure named 'Tenshu' built by Nobunaga ODA in Gifu-jo Castle.
天守は、初期では主に住宅としての機能が重視され、織田信長によって岐阜城に建てられた「天主」と名づけられた四階建の建物のように曲輪の塁上に建てない構造であることもあった。