The Japanese Sengoku period from the mid-15th to early 17th century was a time of nearly continual military conflict. Powerful military lords known as "daimyōs", such as Oda Nobunaga, Toyotomi Hideyoshi or Tokugawa Ieyasu, struggled to unify Japan. During the Sengoku period, because of constant warfare, many fortifications and castles were built. Archetypal Japanese castle construction is a product of the Momoyama period and early Edo period.
A new era of castle construction began when the daimyo Nobunaga built Azuchi Castle from 1576 to 1579. Earlier fortifications of the Kamakura and Muromachi periods were crude large-scale structures; Azuchi, however, with rich ornamentation and a keep rising seven stories high, became the prototype for castle construction of the period. The style of Azuchi Castle marked a shift in the function of the castles from a place that was merely a fortress and military garrison to a political, cultural and economic center. The newer style castles functioned as home to the "daimyōs", his family, and his most loyal retainers. Because of the expense of building such a lavish structure, castles in the style of Azuchi, functioned also to highlight the power and prestige of the "daimyōs". These new castles were built of wood and plaster on a stone foundation. Generally the main keep or "tenshu" was positioned at the highest point, surrounded by a series of interlocking baileys with walls, small towers and pathways. Residential buildings were located in one of the outer circles. The "daimyō" conducted his business in the citadel.
Almost 100 major castles were built between 1596 and 1615. The peak of castle-building occurred during the years 1600 to 1615: in 1600 Tokugawa Ieyasu defeated the Toyotomi clan in the Battle of Sekigahara; and in 1615 the Toyotomi forces were finally destroyed in the siege of Osaka. The Tokugawa shogunate then limited the number of castles to one per province; and banned the building of new castles entirely in 1620. By the time of the Meiji Restoration in the late 19th century, castles were in a state of disuse and neglect. Seen as symbolic of the ruling elite of previous eras, some castles were dismantled and sold as firewood. Others were destroyed by fire, earthquake or typhoon. Only twelve castles have a "donjon" that is considered original.
The term "National Treasure" has been used in Japan to denote cultural properties since 1897.
The definition and the criteria have changed since the inception of the term. These castle structures adhere to the current definition, and were designated national treasures when the Law for the Protection of Cultural Properties was implemented on June 9, 1951. The items are selected by the Ministry of Education, Culture, Sports, Science and Technology based on their "especially high historical or artistic value". This list presents nine entries of National Treasures from five castles built during the late Momoyama to early Edo period; however, the number of structures is actually more because in some cases multiple structures have been combined to form a single entry. The structures listed include "donjon", watch towers and connecting galleries.
In addition to the primarily defensive structures at these five castles, there are also six structures in Nijo Castle's Ninomaru Goten complex, a fortified palace complex located in the castle’s second or outer bailey (Ninomaru) that have National Treasure status. Because these palace structures are listed as residences by the Japanese cultural authorities, Nijo Castle is often not listed as a castle with national treasure structures. However, as goten (castle palaces) were the central and arguably most important feature of Japanese castles, the palace is a historical part of Nijo Castle. In spite of its residential classification, Ninomaru Goten was actually used primarily for administrative purposes. The Ninomaru Goten structures are not included in the list below. 
Features.
The nine national 
treasures on this list are distributed over five castles as follows: Himeji Castle has five national treasure structures; Hikone Castle, Inuyama Castle, Matsue Castle and Matsumoto Castle each have one. Three main types of 
castles exist. Generally the types are characterised according to the 
topography of the castle's site and named accordingly: 
, which are 
castles built on hills in a plain such as Himeji Castle, Hikone Castle, Inuyama Castle, and Matsue Castle.
The 
"donjon" can be constructed in two ways. In the older 
 style, the top of the main keep is formed by a type of lookout tower placed on top of one or more hip-and-gable 
("irimoya") style roofs. Hikone Castle, Himeji Castle, 
Inuyama Castle and Matsue Castle are representative of this style. The 
 style represented by the keep of 
Matsumoto Castle has a virtually square foundation. Each level is slightly smaller than the one below but maintains the same shape.
Only in rare cases the 
"donjon" stands independent of other structures. Generally it is 
connected to smaller watch towers called "yagura", either directly () or via a in which case the style is called 
. Matsumoto Castle has both styles, "renketsushiki" in the northwest 
and "fukugōshiki" in the southeast. At Himeji Castle three watch 
towers, four connecting galleries and the main "donjon" enclose a 
small courtyard.
A typical keep would have between three and seven stories discernible from the outside. Its inner structure including the number of floors could differ from the outward appearance. Castle towers at Himeji, Inuyama, Matsue and Matsumoto Castle have one floor more than is visible from the outside.
Usage.
The table's columns (except for Image) are sortable pressing the arrows symbols. The following gives an overview of what is included in the table and how the sorting works.
References.
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Bibliography.
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