Tenshu (天守) refers to a structure that became the symbol of a castle after the Sengoku period (period of warring states). Such words as 殿主, 殿守, 天主 are also used to refer to Tenshu.
For details of the Tenshu of a specific castle, see the section under the castle.
Presently existing Tenshu will be roughly described here; for further details, see 'Genzon Tenshu' (existing castle tower).
For a list of items for: existence, year of destruction by fire, year of reconstruction, not-existing/now existing/reconstructed, and so on for the Tenshu of each castle, see 'List of Tenshu.'
Tenshu as a term will be described in the following items.
The generally used term is Tenshukaku (keep or tower), a reference which appeared around the Meiji period. 'Tenshu' is used as an academic term in the field of architecture. Tenshu was sometimes regarded as the largest Yagura (turret) in a castle and in some castles was called Oyagura (big turret) or Tenshu-Yagura turret. Today, a three-story turret of a castle without a Tenshu as described later is also categorized as a Tenshu, as is a similar Yagura serving as a symbol; they are sometimes collectively called "Tenshu structure."
Apart from the special cases of Tenshu of Azuchi-jo Castle in the Tensho era and Osaka-jo Castle, which were used as living quarters, Tenshu of many castles in Japan came to be used as lofts around the Edo period, and Nagoya-jo Castle Dai-Tenshu (large keep) was little used and gradually came to be an empty house. Therefore, Tenshu was not such a residence as Seiden (main palace) symbolic of a Chinese castle but closer to a keep tower of a European castle.
Tenshu of two-tier to five-tier structures in appearance were seen in large numbers and, at the end of the Azuchi-Momoyama period, many were constructed at Honmaru (the most important castle enclosure) deemed to be the final protective stronghold. There were Tenshu surrounded by additional enclosures in Honmaru, which were called Tenshukuruwa and Tenshumaru.
Castles without Tenshu
Even in the early-modern times (after the Azuchi-Momoyama period), many castles did not even have Tenshudai (base of keep); construction of Tenshu having been judged unnecessary from the start. In the Edo period, a growing number of Tenshu in castles were not reconstructed after being destroyed by fire. Also, there were some castles with Tenshudai on which Tenshu were not constructed for some reason.
In the following four situations, Tenshudai and Tenshu were not constructed in the Edo period.
Tenshu was destroyed by fire or collapsed, but after that, reconstruction was judged unnecessary (Edo-jo Castle, Osaka-jo Castle, and so on).
Tenshu was destroyed by fire or collapsed, but after that, due to deference to the Bakufu or economic difficulties, was not reconstructed (Kanazawa-jo Castle, Fukui-jo Castle, Saga-jo Castle, and so on).
Tenshudai was constructed with intention to construct Tenshu, or construction of Tenshu was planned, but it was not realized due to deference to the Bakufu or economic difficulties (Fukuoka-jo Castle, Ako-jo Castle, and so on).
Tenshu and Tenshudai were not constructed in the castle (Yonezawa-jo Castle, Sendai-jo Castle, and so on).
Many of the above castles used or constructed Sanju Yagura (Three-tiered turret) and Sumi-Yagura turret instead of Tenshu under the pretext of Gosankai Yagura (Three-storied turret), while there were castles which did not have these (Kagoshima-jo Castle, Hitoyoshi-jo Castle, and so on).
Gosankai Yagura and Tenshu substitutes
Gosankai Yagura (also known as Osankai Yagura) refers to three-story Yagura in the castles where construction of Tenshu was prohibited or not performed due to Buke shohatto (Laws for the Military Houses) and Ikkoku Ichijo Rei (Law of One Castle per Province) promulgated in the Edo period. These were 'Virtual Tenshu,' which were called that to avoid the name "Tenshu" in deference to the Bakufu. Depending on the castle, it was also called Gosankai (Kokura-jo Castle), Oyagura (big turret) (Shiraishi-jo Castle), Sanju Yagura (Shirakawa Komine-jo Castle), and so on. Regardless of the names, some were five-story and four-story inside, such as Kanazawa-jo Castle and Mito-jo Castle. There are some which were renamed Tenshu, such as the one in Morioka-jo Castle. Although many were constructed in Honmaru as Tenshu were, some were constructed in Ninomaru (outer citadel) as Gosankai Yagura in Tokushima-jo Castle and Mito-jo Castle were. Presently existing Gosankai Yagura include Hirosaki-jo Castle keep and Marugame-jo Castle keep.
In many cases, the structures often called Tenshu substitutes indicate 'Virtual Tenshu,' and multiple-story Yagura, which are sometimes treated as Tenshu depending on their scale and design (Kurume-jo Castle tatsumi three-story turret, Fukui-jo Castle three-story turret and so on). The multiple-story Yagura so recognized include not only Sanju Yagura such as Gosankai Yagura but also Niju Yagura (two-story turret). However, the above situation indicates that Sumi-Yagura turret and Yagura with special functions were deemed to be symbolic structures instead of Tenshu, so these Yagura are sometimes not recognized as Tenshu as Gosankai Yagura are. Also, there were not only Yagura but also a Tenshu substitute such as 'Odashishoin' of Kubota-jo Castle, which was a Goten (palace) constructed on Honmaru foundation.
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. Afterwards, usage as living quarters and guest house was considered important also for Tenshu of Azuchi-jo Castle and Osaka-jo Castle, and in the Keicho era, Tenshu with a feature of Shoin-zukuri style (a traditional Japanese style of residential architecture that includes a Tokonoma), such as Okayama-jo Castle keep and Kumamoto-jo Castle keep, were constructed. On the other hand, Tenshu emphasizing gorgeous appearance and with as simple interior as possible, such as Nagoya-jo Castle keep by Ieyasu TOKUGAWA and Hiroshima-jo Castle keep, appeared, and it is considered that, thereafter, the function of a building into which the lord or guests enter started to disappear from Tenshu. After that, many Tenshu were empty and quite a lot of Tenshu were used as lofts.
Ten good points and purposes were described in the 'Ten virtues of Tenshu' in the military science of the Edo period.
Look over the inside of the castle
Look onto the outside of the castle
Look onto the distance
Place warriors freely inside the castle
Pay attention to the inside of the castle
Command freely in defense
Look over the enemy's invasion
Defend freely against projectile weapons
Control battle plans freely in emergency
Serve as a symbol of the castle
No conclusion has been reached on the origin of the name and style/type.
It is considered that, early on, Tenshu featured the functions of Monomi-Yagura turret, control tower, and the final protective stronghold, but, from around the time of suppression of the Kinki region by Nobunaga ODA, Tenshu gradually came to be a structure symbolic of strong power which could be seen from a distance.
Yasuhiro NISHIGAYA regards the origins of the structure symbolic of a castle to be such temporary high-rise buildings as lookouts found in the Yoshinogari site and so on and watch towers and so on in the Sengoku period. A building constructed as a symbol which was first called "Tenshu" was the Tenshu constructed in Muromachi-dai (the mansion of the Ashikaga family) which was Gosho (palace) of the 15th Shogun Yoshiaki ASHIKAGA of the Muromachi bakufu (Japanese feudal government headed by a shogun).
On the other hand, Masayuki MIURA regards the origins of Tenshu to be permanent high-rise buildings of large scale constructed on the foundation stone in castles of the Medieval period instead of watch towers. He also indicates the structures which were called "Tenshu" as being related to Nobunaga.
It is generally said that the allegedly first full-scale Tenshu of five tiers or more which can be seen today was the Tenshu constructed by Nobunaga ODA in 1579 in Azuchi-jo Castle (Azuchi-cho, Shiga Prefecture).
However, symbolic structures like Tenshu were not absolutely nonexistent before Azuchi-jo Castle was built; examples from various places include Seishoken of Dokan OTA which had been in Edo-jo Castle around 1469, Settsu Province Itami-jo Castle (Itami City, Hyogo Prefecture), Yamato Province, Tamonyama-jo Castle built by Hisahide MATSUNAGA in the Eiroku era (1558-1569), and the Yonkai Yagura (four-story turret) in Shigisan-jo Castle.
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.
Origin of the name
The name is considered to have originated from Densu and Tenshu, or also to have been given by religious thought such as Buddhistic thought or by a corruption of Tenshu (Deus, which means Zeus) of Christianity.
According to Shigetaka MIYAKAMI, the name Tenshu originated from Tenshu of Gifu-jo Castle, where Nobunaga ODA, requesting Shuryo SAKUGEN, gave the name to a four-story palace understood to be located at Fumoto (the foothill).
Hideyoshi TOYOTOMI further popularized so-called Tenshu, symbolic multiple-story buildings which had been so constructed. After the gorgeous Tenshu of Osaka-jo Castle and Fushimi-jo Castle were constructed in succession by Hideyoshi TOYOTOMI, Daimyo (feudal lord) in various places imitated this and built high-rise Tenshu in their own castles. Tenshu is pointed to as one of the features of Shokuho period fortresses, because Tenshu were seen in great number in 'Shokuho period fortresses' developed under the Shokuho government of Nobunaga ODA and Hideyoshi TOYOTOMI ("Shoku" and "ho" are the initial letters of Oda and Toyotomi). Experts who participated actively in Tenshu construction in that period included Masakiyo NAKAI and Mataemon OKANO.
When the Toyotomi government began falling off, Ieyasu TOKUGAWA and territorial lords started to construct large-scale, decorative Tenshu, including Tokugawa Nagoya-jo Castle and Himeji-jo Castle, which surpassed Toyotomi Osaka-jo Castle. However, after Iemitsu TOKUGAWA, the third Shogun, promulgated Buke shohatto, high-rise Tenshu structures with the name of 'Tenshu' ceased to be constructed.
Due to Tenshu height restriction imposed by Ieyasu TOKUGAWA around 1609, only powerful Kunimochi Daimyo (a feudal lord having domain of one province or more) were permitted to construct Tenshu of five or more tiers. After that, some Daimyo refrained from constructing five-tiered Tenshu, and in the case of Kokura-jo Castle (1610) which was built after that, the fourth-tier roof was taken away and the floor of the fifth story was protruded in order not to make it five-tiered. Due to Ikkoku Ichijo Rei promulgated by Tokugawa Shogunate in 1615, new construction and renovation/repair of a castle were not allowed without the Bakufu's permission, and new construction of Tenshu was also prohibited without permission. After this, in a similar way, some were constructed as virtual five-tiered Tenshu but made as nominal four-tiered ones, regarding the fourth-tier roof as Hisashi (eaves), as in the case of Tsuyama-jo Castle (1616) and Fukuyama-jo Castle (Bingo Province) (1622), and some were constructed as five-story Tenshu inside but made to appear three-tiered from the outside as in the case of Takamatsu-jo Castle (Sanuki Province) (1669). Also, some five-tiered Tenshu were reconstructed into three-tiered ones, as in the case of Matsuyama-jo Castle (Iyo Province) in Iyo Province. Some constructed large-scale Sanju Yagura with Tenshu in mind but refrained from naming them Tenshu and called them Gosankai Yagura and so on.
With the dawning of the Edo period, peace came and the defensive role of castles was gradually changed to the role as government offices; thus, the role of Tenshu was also finished, and Goten and Ninomaru/Sannomaru were gradually expanded in castles.
From Meiji period
After the Meiji Restoration, most of the structures including Tenshu which were in castles and Jinya (regional government office) were disposed of by the private sector or by government as requisitioned military facilities/land and knocked down; however, some Tenshu were conserved as a result of the civic movement and approaches by public officials/military personnel for conservation. Inuyama-jo Castle keep came to be conserved because the castellan continued to be the owner of the castle, and the buildings in Himeji-jo Castle were said to be left unharmed because the private sector (individual) was not able to pay expenses for demolition work; these were rare examples. The number of Tenshu conserved that way was only 21, including Shuri-jo Castle main hall in Okinawa. After that, eight castles, including Shuri-jo Castle, burned down during domestic conflicts such as the Seinan War and, at the end of the Pacific War, bombing on Japan's mainland and in the Battle of Okinawa, and, after World War II, Matsumae-jo Castle keep was destroyed by an accidental fire; as a result. there are only 12 Genzon Tenshu today. Projects were actively going on after the War to externally restore, by concrete, Tenshu designated as national treasures which had burned down in the Pacific War and, even today, there are movements to restore the ruins of castles including Tenshu by the building methods of those days.
Tenshu needed to have not only structural practicality, including protective quality, fire resistance, and quake resistance as a usual Yagura, but also decorative quality as a symbolic structure. Many Tenshu sometimes adopted special design to show social status. The following describes designs/structures seen on symbolic structures mainly including Tenshu and large-scale Yagura, regardless of whether they were Borogata (lookout tower type keep) or Sotogata (multi-leveled tower type keep).
Tenshudai (base of keep)
Takadai (elevated ground) (Yagura-dai and so on) with piled-up Dorui (earthwork) and stone wall is called Tenshudai. According to the situation of each castle, there were differences in scale and shape, and some were high and some were low. Some Tenshu were constructed directly on a foundation stone put on the ground of the castle, rather than on a Tenshudai. The inside of some Tenshudai were made hollow to provide an underground floor called Anagura (cellar).
Moya (the central space under the main roof of the Shinden hall) and Irikawa (corridor-like peripheral space surrounding a room)
In many cases, differing from small-scale Yagura, tenshu included a Corridor, Irikawa, which is under the Geya, and inner-side Moya, which is the main space. These structures were omitted not only in Tenshu but also standard-scale Yagura in many castles, and they were mainly constructed only in large-scale buildings such as Tenshu.
Hafu-beya (gable room)
It was a Koyaura-beya (room in the space between a room and a ceiling) inside Hafu, which had a function of a bay window. In more recent years, the room came not to be constructed. It was constructed in not only Tenshu, but, in few cases, also in large- and small-scale Yagura.
It was a structure, the first tier of which was protruded from Tenshu/Yaguradai (base of Yagura), and Ishiotoshi (a boulder drop) was constructed on the floor of the protruded part. It was able to be constructed in neat shape regardless of distorted Tenshudai/Yaguradai and was also considered to be effective in defense and offense.
It refers to the design of a roof including gable wall and gable board. It was high in decorative value, and the small room (Hafu-beya) constructed inside had important functions in both defense and offense.
Nageshi-gata (a horizontal piece of timber pattern)
It was a wall design to make a Shikkui (plaster) Okabe (whole surface of wall) look like a Shin-kabe (a type of plastered wall in which structural members are exposed) (structure) by having the shapes of pillars and Nageshi stand out on the Shikkui wall. It was seen in some Yagura.
Mawarien (cornice) and Koran (a balustrade or railing which adds a decorative element)
It was a kind of go-around veranda (a narrow wooden passageway along the edge of a house facing the garden) constructed on the top story and, in one case, from which they were able to go out (Soto (Outer)-Mawarien)), a highly-decorated Koran (handrail and balusters) was attached. Uchi (Inner)-Mawarien was created if the veranda was bratticed from the outside by a wall or panel. A peculiar kind called Kara-zukuri style was also constructed. Impractical Soto-Mawarien is sometimes called Kazari (Decorative)-Mawarien-Koran.
In many cases, it is called 'Shachihoko.'
These were, in many cases, made of wood or tile and put on the Omune ridge of the top story. They were, in many cases, put on the top of not only Tenshu but also major Yagura.
Exterior finish of walls
Exterior walls of Tenshu were decorated by Shitamiita-bari (weather-board lined) of black lacquer, Kuroboku soils (black soils rich in humus content) or persimmon juice coatings, or Okabe finishing of Shikkui-nurigome (solid plastered fire-resistant wall). In addition, some Tenshu were finished by Hameita-bari (a clapped-wood lining) seen on the structures including Kochi-jo Castle Otte-mon Gate (Main Gate), the above-mentioned Nageshi-gata Shikkui-kabe (plaster wall) and Namakokabe (a wall with square tiles jointed with raised plaster) for walls in the cold regions.
In the past, there was a view that Tenshu with Shikkui-Okabe (Plaster wall) were more in a newer style than Tenshu with Shitamiita-bari; however, recently there is an opinion that they are equal with each other.
In some castles, small multiple-tiered Yagura were called Sho-Tenshu (small keep) or Fuku-Tenshu (small keep) and Tenshu that were intermediate in scale between Tenshu and Sho-Tenshu were referred to as Chu-Tenshu (medium keep), and if there were more than one Sho-Tenshu as in the case of the group of Tenshu in Himeji-jo Castle, each of these was given a prefix indicating direction. If there were many Tenshu, the large Tenshu were, in many cases, called Dai-Tenshu (large keep). Yagura annexed to a major Yagura were called Tsuzuki-Yagura (linking turrets) and Yagura attached to Tenshu were called Tsuke-Yagura (attached tower). Sometimes they were called Fuzoku-Yagura (attached tower).
These expressions are used to describe the status and roles of the structures; however, not all of the currently used expressions have necessarily been used historically in these castles.
Tenshu is enumerated by 'Ki' as in the case of Yagura, but sometimes by 'To/Mune' as in the case of ordinary housing.
Numeration for story and tier
The castle structures, mainly Tenshu and multiple-tiered Yagura, were, in many cases, constructed with the roofs being piled up in a complicated way, and when story and tier should be identified, the numeration for ordinary housing, simply '-story,' may make the enumerated data improper for knowing the outline of the castle structures. Therefore, whether complicated or not, it is recommendable to use "So" (tier) or "Ju" (tier) indicating the number of roofs in appearance and "Kai" (story) indicating the number of internal floors, to be laid side-by-side like '-So (tiered) -Kai (story)' and '-Ju (tiered) -Kai (story) (Example: Three-tiered, five-story).
Kai and Ju were, in many cases, used independently in books, Kuden (oral tradition), and legends, and there was no unified standard in numeration of story and tier, which indicates a possibility of the expressions being handed down as local ones. Therefore, even if a structure came down as a three-story turret, it was not always three-story but could have been five-story, and even if it came down as Goju-Tenshu (five-tiered Tenshu), it could have been the number of floors inside and in reality four-tiered or three-tiered in appearance. Sometimes underground floors were enumerated. Therefore, the numeration of story and tier in the books and Kuden is not considered to be compatible with the current way of numeration for the internal and external appearances.
Differences among researchers
Numeration differs, depending on researchers and scholars. The following are from the descriptions made by Yasuhiro NISHIGAYA and Masayuki MIURA.
Yasuhiro NISHIGAYA adopts '-tiered -story' and indicates that So (tier) is for the number of roofs, Ju (tier) for that of floors, and Kai (story) for that of floors excluding basement (aboveground floors). This is because he followed the numeration adopted by The Japan Association for The History of Castles under his presidency and he pointed out the defect of numeration by So (tier).
Masayuki MIURA uses '-Ju (tiered)-Kai (story)' and explains that Ju is for the roofs in appearance and Kai for the internal floors. In addition, he indicates So (tier) can be used instead of Kai (story) and does not recommend the use.
At any rate, if '-So (tiered)-Kai (story),' '-Ju (tiered)-Kai (story),' '-Ju (tiered)-So (tiered)' and so on are used in the same document, the text itself would become difficult to understand, so such a parallel use as above is, in many cases, avoided in books and so on dealing with the Japanese castles.
Tenshu are classified roughly into two types, Borogata (lookout tower type keep) and Sotogata (multi-leveled tower type keep). However, as for the sequence of development, no conclusion has been reached about which of Borogata or Sotogata was first.
Tenshu are divided into Borogata and Sotogata in structure, and as for the externally peculiar ones, although there is no particular standard, they are sometimes further divided into Fukko (revival), Ryakushiki (informal), Kara-zukuri, Yatsumune-zukuri (a complicated roof style with multiple ridges and bargeboards, or large vernacular house built in this style) types, and so on. Tenshu externally restored or reconstructed in modern times with the existing methods rather than the original methods sometimes came under a different structural category, because the appearance of that time was restored by imitating the original situation and structure but the inner structure was not reconstructed by the original methods. However, these Tenshu are also classified into Borogata and Sotogata in appearance. Borogata and Sotogata in this text are based on the category mainly in structure.
Early period and later period
The division into the early and later periods is done by era/development, decrease rate of plane scale, and improvement of the Shoju (the first story) plane, and not by structural development. This rigid division is not necessarily followed by everyone; for instance, Masayuki MIURA and Masafumi KATO use expressions such as 'Traditional Borogata' and 'Typical Sotogata' instead of these terms.
Borogata is a type like a small-scale Boro put on top of Yagura of Irimoya-zukuri (a hip-and-gable roof construction, or a building with this roof construction). It was constructed, in many cases, in the shapes like Boro put on top of the Hira-Yagura turret of Irimoya-zukuri and Boro put on top of Niju Yagura of Jubako-zukuri on the Irimoya roof. Boro was put, as a separate structure, on Yagura of Irimoya-zukuri, so even if the ground surface under Shoju was distorted, the above tiers on top of it were able to be maintained rectangular. Since Hafu, one of the features of Tenshu, was surely created, it became a magnificent design. More particularly, Borogata is sometimes divided into early Boro and later Boro. Tenshu, the Boro part of which was constructed small with high rate of decrease in roof size, are regarded as early period ones, including the Tenshu of Inuyama-jo Castle and Maruoka-jo Castle, which are understood to have been constructed before the Battle of Sekigahara. Tenshu, whose rate of decrease in roof size became low and the Boro part of which became low in function as watchtower, were, in many cases, constructed after the Battle of Sekigahara and these are regarded as later period ones; examples include the Himeji-jo Castle keep. Regardless of their structure and external design, Tenshu are sometimes divided by their construction time into the periods before or after the Battle of Sekigahara.
Mainly before the Battle of Sekigahara
Hiroshima-jo Castle large keep
Okayama-jo Castle keep
Matsumoto-jo Castle large keep
and so on.
Genzon Tenshu, of which structure can be identified
Maruoka-jo Castle keep
Inuyama-jo Castle keep
Mainly from the Battle of Sekigahara to Kanei era
Kumamoto-jo Castle large keep
Hagi-jo Castle keep
and so on.
Genzon Tenshu, of which structure can be identified
Hikone-jo Castle keep
Himeji-jo Castle large keep
Matsue-jo Castle keep
and so on.
They were seen mainly after the Kanei era and had a sense of top-to-bottom unity in design, like a five-storied pagoda of a temple.
The plane scale of this type gradually decreases upward and only the roof of the top tier was made Irimoya. Chidori Hafu (a triangular shaped gable or a dormer bargeboard, or both combined) and Kara-Hafu (literally, Tang gable) were attached to them, but Oirimoya (big Irimoya) which could have directly become a base were not constructed, and there were ones without any Hafu. Shoju of Sotogata Tenshu of early period were sometimes constructed large regardless of plane decrease.
Nagoya-jo Castle keep
Kokura-jo Castle large keep
Fukuyama-jo Castle (Bingo Province) keep
and so on.
Genzon Tenshu, of which structure can be identified
Hirosaki-jo Castle keep (Gosankai Yagura)
Matsuyama-jo Castle (Iyo Province) large keep
Uwajima-jo Castle keep
Classification by appearance
In addition to the classification into Borogata and Sotogata in structure, Tenshu are classified in appearance by various factors. However, these categories are not necessarily official ones and some researchers and scholars may sometimes use unique expressions.
Fukko type were Tenshu, the appearance of which was made closer to the original or old-fashioned ones. These Tenshu were reconstructed by permission of the Bakufu in the mid Edo period to the later Edo period. Sotogata was the mainstream around the mid Edo period, but there were both Borogata and Sotogata in structure. Among other things, the original burned-down Borogata Tenshu of Kochi-jo Castle is said to have been accurately reconstructed, and Matsuyama-jo Castle (Iyo Province) large keep is the last Momoyama-style Sotogata Tenshu reconstructed in Japan.
Wakayama-jo Castle large keep
Okazaki-jo Castle large keep
and so on.
Genzon Tenshu, of which structure can be identified
Kochi-jo Castle keep
Matsuyama-jo Castle large keep
Haridashi and Hanedashi-zukuri
Haridashi or Hanedashi-zukuri is a Tenshu, the Shoju plane of which was constructed larger than the Tenshudai plane. They were designed to eliminate distortion of the plane shape seen on the Tenshudai of the early period. It was possible to cut open a part of the floor to make it a boulder drop.
Hagi-jo Castle keep
Kumamoto-jo Castle large keep
Takamatsu-jo Castle keep
Nawabari (castle plan; general term for the layout of a castle and its component structures)
The nawabari type of Tenshu is divided into four types, Dokuritsu-shiki (independent), Fukugo-shiki (directly connected), Renketsu-shiki (connected), and Renritsu-shiki (combined) types.
The sequence of the above listing does not necessarily indicate the development sequence of the types.
Tenshu after Meiji period
In 1873, the Ordinance abolishing castles was promulgated and many structures in castles were lost. Even after the promulgation of the Ordinance, over 60 Tenshu existed; however, the compounds of castles were taken over by the army and became army posts, and so Tenshu were progressively knocked down. In addition, during World War II, the US military forces regarded the castles as military facilities and attacked them from the air, and so many more were lost.
Twelve Tenshu constructed before the Edo period have survived to the present time in Japan. Four were designated as national treasures, including Himeji-jo Castle, which was registered as a World Heritage Site, and all of the remaining eight Tenshu were designated as national important cultural properties. These are called Genzon 12 Tenshu (Twelve Genzon Tenshu), Kokuho Yonjo (Four national-treasure castles) and Jubun Hachijo (Eight national-important-cultural property castles) (Jubun Hachi Tenshu (Eight national-important-cultural property Tenshu)) (For details, refer to the separate section, 'Genzon Tenshu').
Modern/contemporary construction of Tenshu
After the Meiji period, along with abolishment of castles themselves, structures including Tenshu were not constructed when castles were constructed, but structures similar to Tenshu and reconstructed 'Tenshu' of old castles appeared. When the Showa period began, Tenshu started to be restored or constructed, mainly for the purpose of regional developments.
It was especially after World War II that Tenshu started to be actively constructed and, in many cases, those which had been burned down by air-raid, shown in old photographs or depicted in drawings or were only in legend were constructed in the reinforced concrete structure. As many of those Tenshu were constructed on the ancient foundations, foundation stones were moved and stone walls were rebuilt.
More especially, in regard to imitation Tenshu and reconstructed Tenshu/externally restored Tenshu which were constructed by modern building methods, some expressed concern about 'the possible destruction of historical heritage.'
In the Heisei period, the number of Tenshu constructions with by concrete and so on has decreased, and along with the Agency for Cultural Affairs, which has made its policy for restoration stricter, the number of more accurate restorations with wood, such as Kakegawa-jo Castle and Ozu-jo Castle, has increased.
Tenshu constructed in modern/contemporary times are divided into the categories of restored Tenshu (復元天守) (also written as 復原天守) (restored wooden Tenshu and externally restored Tenshu), reconstructed Tenshu, imitation Tenshu, and Tenshukaku-style structure. In addition, restored Tenshu and reconstructed Tenshu are sometimes collectively referred to as rebuilt Tenshu.
Restored Tenshu (復元天守) (also written as 復原天守)
It refers to a Tenshu which was lost by fire, natural disaster, knockdown, or war damage (including damage by nuclear weapons) and restored to its original state at least in appearance. They are mainly Tenshu which were lost in World War II. It is further divided into restored wooden Tenshu and externally restored Tenshu. The Agency for Cultural Affairs-indicated 'Restoration' refers only to wooden restoration. The Tenshu which was most recently restored among all of the restored Tenshu is Ozu-jo Castle keep, which was completed in 2004.
Construction of wooden buildings of four-stories or more was restricted by the Building Standard Act Enforcement Order, which required use of diagonal beams and metal materials and adoption of a concrete foundation, and also by the Fire and Disaster Management Act. Even if Tenshu restoration in a strict sense was planned,it was impossible to comply with the earthquake-proof standard and the safety standard for the use of buildings. Therefore, it was, in many cases, unavoidable for Tenshu to be constructed in the reinforced concrete structure even if enough information to justify restoration of Tenshu was available, and it was only possible to construct wooden Tenshu by getting special permission of the Minister of Construction or by exploiting legal loopholes as in the case of Gosankai Yagura of Shirakawa Komine-jo Castle. After the Heisei period set in, Tenshu came to be actively constructed by construction methods as close to traditional methods as possible under the guidance of the Ministry of Construction.
While restoration of Tenshu is restricted by the Building Standard Act and the Fire and Disaster Management Act, reconstruction in the national historic sites is permitted by the Agency for Cultural Affairs on the basis of 'Charter for the Protection and Management of Archaeological Heritage.'
Therefore, reconstruction may be approved as an exemption from the Building Standard Act and as an exception of the Fire and Disaster Management Act as in the case of Ozu-jo Castle keep.
Restored wooden Tenshu refers to Tenshu which were accurately restored to their original state with the same materials (kinds of wood), configuration type, and construction methods on the basis of then-surviving drawings, written records, ancient structural remnants, and so on around that time. The first restored wooden Tenshu as equivalent to Tenshu is Shirakawa-jo Castle three-story turret restored in 1990. Ozu-jo Castle keep is only one which was perfectly restored as Tenshu, and Shuri-jo Castle main hall is the only one equivalent to Tenshu at this point of time.
Externally restored Tenshu refers to Tenshu which were restored to their state of the bygone days only externally in the steel framed reinforced concrete structure and so on. The first Tenshu of this type was Nagoya-jo Castle (Nagoya City, Aichi Prefecture, restored in 1957).
Partly because the criteria and examinations became gradually stricter regarding restoration of structures around that time in the historic castle sites, which were regulated by the Agency for Cultural Affairs, externally restored Tenshu with modern materials and construction methods should, in a narrow sense, be included in the category of reconstructed Tenshu. Although they are called externally restored Tenshu, it was inevitable for some Tenshu to be different in details such as the scale, place, and shape of their windows or the curving degree of their roofs as a result of the requirement to comply with the Building Standard Act. It is said that there are no Tenshu which were accurately restored externally, because they were changed in their details, for the purpose of tourism and so on. For instance, Tenshu of Ogaki-jo Castle and Nagoya-jo Castle, which were externally restored after the War almost followed the appearance before the War; however, the windows of the top tier were reconstructed a little larger than they were in the bygone days, considering the function as an observation platform.
It refers to a Tenshu which surely existed in the past but was afterward lost by fire, natural disaster, knockdown, or war damage and was reconstructed at the original location but with assumptive part in scale and design due to an intention not to be based on the historical facts and due to lack of historical data. This type includes Tenshu which were given such attachments as affecting the image of their appearance. For example, Kokura-jo Castle reconstructed Tenshu, which had been Sotogata without Hafu under the roof, was reconstructed as Borogata adding Hafu. Reconstructed Tenshu of Odawara-jo Castle and Okazaki-jo Castle, which differed in the size of their windows and were given Koran, are sometimes classified into this category, and sometimes into externally restored Tenshu, deeming these inaccuracies acceptable.
The first Tenshu of this type was Gifu-jo Castle, which is said to have been reconstructed in 1910 with historical data on Kano-jo Castle Gosankai Yagura used for reference. The current Gifu-jo Castle was reconstructed after it had burned down by air-raid. The first reconstructed Tenshu in the steel framed reinforced concrete structure was Osaka-jo Castle Tenshukaku (Osaka City, Osaka Prefecture) reconstructed in 1931 in Osaka-jo Castle. The first reconstructed Tenshu after World War II was Kishiwada-jo Castle (Kishiwada City, Osaka Prefecture), reconstructed in 1954. This type were usually reconstructed in the reinforced concrete structure, but some were in the wooden construction, such as Kakegawa-jo Castle.
It refers to Tenshu constructed in castles where no Tenshu had existed or where Tenshu had existed but were missing. It is sometimes called a reconstructed imitation keep. Tenshu which surely existed in the past but were not based on historical facts and reconstructed at a different location are classified into this category. It also includes Sanju Yagura and so on. Some Tenshu of this type were constructed with the appearance designed independently; on the other hand, many Tenshu were constructed after the model of Tenshu of Inuyama-jo Castle and Ogaki-jo Castle. Some of them are structures designed without consideration for the historical background of the architectural style.
It refers to Tenshu constructed at the following locations.
Castles where no Tenshu existed and castles where Tenshudai existed but no Tenshu was constructed (Sunomata-jo Castle, Toyama-jo Castle and so on)
Castles where the existence of Tenshu is not known (Imabari-jo Castle, Kaminoyama-jo Castle and so on)
Tenshu constructed at locations other than the original locations (Fushimi-jo Castle, Kiyosu-jo Castle, and so on)
The first Tenshu of this type was Sumoto-jo Castle (Sumoto City, Hyogo Prefecture), constructed in 1928 and the oldest of the currently existing Tenshu including restored Tenshu and reconstructed Tenshu. In the Showa period after the War, Tenshu of Toyama-jo Castle (Toyama City, Toyama Prefecture). This type were usually reconstructed in the reinforced concrete structure, but some were in the wooden construction, such as the Imitation Tenshu of Iga Ueno-jo Castle, Gujo Hachiman-jo Castle, and Aya-jo Castle.
It refers to Tenshu which were constructed imitating the design of Tenshu in the locations where no castle existed, or in urban areas, etc. It is called Tenshu style architecture or Tenshu style building. This type is not classified strictly and so some Tenshu are classified into Imitation Tenshu, such as Fushimi Momoyama-jo Castle. Although some university museums, tourist facilities such as theme parks and exhibition facilities, community facilities such as city halls, private houses, and stores in Japan and overseas have adopted Tenshukaku-style for their structures, their peculiar appearance became a target of criticism. However, for some of these, special attention was paid to not only appearance but also the details of structures.