While castles in which such a structure as Tenshu were first built are unknown, Itami-jo Castle, Gakuden-jo Castle, Tamonyama-jo Castle, and so on have been listed as Tenshu first seen on the grounds of ancient documents and so on; however, specific ancient structural remnants have not been found for these structures and it is difficult to prove that they were Tenshu first seen.
天守のような建物が初めて造られた城はわかっておらず、伊丹城、楽田城、多聞山城などが古文献などを根拠に天守の初見として挙げられているが、具体的な遺構などは不詳であり、いずれも、天守の初見であるとの立証が難しくなっている。