目錄
When you think of a Japanese castle, what kind of image comes to mind? A towering keep rising into the sky, rows of carefully arranged castle walls, or an impregnable defensive system? Japanese castles are more than buildings. They are symbols that carry centuries of history and a distinctive cultural heritage. In this article, we will take an in-depth look at the three most important elements of Japanese castles: stone walls, turrets and keeps. We will explore how these seemingly silent structures tell the story of political power, military ingenuity and aesthetic values during Japan’s Sengoku and Edo periods.
Through this article, you will not only learn about the individual functions and development of these three elements, but also see how closely they were connected and how they worked together to create the distinctive appearance of Japanese castles.
The Soul of a Japanese Castle: Stone Walls, Turrets and Keeps
Japan has a long history of castle culture, and the three elements that best represent its distinctive appearance and functions are stone walls, turrets and keeps. They were not merely defensive structures, but also tangible expressions of the power and military strength of feudal lords, leaving a lasting mark on Japanese history and culture.
The Evolution of Japanese Castles: From Simple Fortifications to Magnificent Keeps
The history of Japanese castles can be traced back to the moated settlements of the Yayoi period and the stone-stacking techniques of the Kofun period. From the Asuka to the Nara period, ancient mountain fortresses were constructed in Kyushu and around the Seto Inland Sea to defend against foreign invasion, and techniques for building stone walls were introduced. However, the large-scale use of stone walls and the construction of castles with multiple defensive layers did not become widespread until matchlock firearms were introduced to Japan during the Sengoku period.
Before the arrival of matchlock guns, Japanese castles relied mainly on earthen embankments and moats for defense. As new weapons created greater threats, stronger fortifications became increasingly necessary. Komakiyama Castle, built by Oda Nobunaga, and Iimoriyama Castle, occupied by Miyoshi Nagayoshi, were among the early castles to incorporate stone walls. After the construction of Azuchi Castle, stone walls became a standard feature of castle building, and masonry techniques developed rapidly. During the time of Toyotomi Hideyoshi, castle construction grew even larger in scale, eventually reaching its peak in the early Edo period. As the highest point of the castle and a final defensive stronghold, the keep became one of the most recognizable symbols of Japanese castles.
The Impregnable Foundation: The Defensive Base and Curved Beauty of Japanese Castles
Stone walls were the most fundamental and essential defensive structures in Japanese castles. They not only provided a stable foundation for the buildings above, but their distinctive curves and sophisticated construction techniques also made them visually impressive works of art.
Why Were Stone Walls Symbols of Power? The Logic of Display from the Sengoku to the Edo Period
The stone walls of Japanese castles demonstrate a traditional building technology and aesthetic found nowhere else in quite the same form. Their structural designs often provided excellent resistance to earthquakes, while their graceful inward-curving profiles created an appearance that was both solid and elegant. During the time of Oda Nobunaga, large-scale castle construction using stone walls became a symbol of a lord’s authority. Toyotomi Hideyoshi expanded castle building to an even greater scale, turning stone walls into more than practical defenses. They became direct proof of a daimyō’s wealth and ability to mobilize labor and resources. Strong stone walls also made it possible to build turrets above them and station matchlock troops inside. Even in rainy weather, defenders could continue to fire effectively, greatly improving the efficiency of the castle’s defenses.
The Engineering Wisdom of Stone Walls: Construction Methods and Earthquake Resistance
Building stone walls involved far more than simply stacking stones. It required highly developed knowledge of civil engineering. Based on the degree to which the stones were processed, the principal construction methods can be divided into the following types:
- 野面積み（Nozura-zumi）: This was the earliest technique. Natural stones were used with very little processing and stacked directly, creating a rugged and primitive appearance.
- 打込接ぎ（Uchikomi-hagi）: The corners and edges of the stones were roughly shaped to reduce the spaces between them and improve structural stability.
- 切込接ぎ（Kirikomi-hagi）: This was the most refined technique. Stones were cut into regular shapes so that they could fit tightly together with almost no gaps, demonstrating a high level of craftsmanship.
In addition to the way the stones were processed, the arrangement of the stones also required considerable expertise:
- 布積み（Nuno-zumi）: Processed stones were arranged neatly in horizontal rows, creating continuous horizontal lines.
- 乱積み（Ran-zumi）: Stones of different sizes were stacked irregularly. Although the horizontal lines were not continuous, this arrangement could help distribute structural pressure.
- 算木積み（Sangi-zumi）: At the corners of stone walls, rectangular stones were stacked by alternating their long and short sides. This effectively strengthened the corners and became one of the most distinctive features of Japanese castle masonry.
Many stone walls were built using the 空積み（Kara-zumi）method, meaning that no mortar or adhesive was used. The stones were held in place only by their weight and carefully calculated arrangement. During an earthquake, the stones could shift slightly and absorb part of the seismic force, demonstrating the sophisticated earthquake-resistant knowledge of Japanese builders. The interior of the stone walls also contained backing stones known as 裏込石（Uragome-ishi）and drainage systems, helping to maintain long-term structural stability and proper water drainage. During 天下普請（tenka-bushin）, castle-building projects in which daimyō from across the country were required to participate, stones were sometimes engraved with family crests or identifying marks to indicate the lord responsible for supplying them, leaving behind another type of historical record.
Marks on Stone Walls: Family Crests, Tenka-bushin and the Political Landscape
The development of stone-wall construction techniques also reflects the technological and cultural characteristics of different periods. From the early use of nozura-zumi to the later development of kirikomi-hagi, stone processing became increasingly precise. This was not only a sign of technological progress, but was also closely connected to the growing wealth of daimyō and their desire to display their authority. For example, the stone walls of early modern castles built after Azuchi Castle were often larger in scale and more carefully constructed, becoming symbols of the castle lord’s status. Family crests and other marks that remain on many stone walls today also offer a glimpse into the political relationships and cooperation between daimyō at the time.
Fortresses of Observation and Attack: The Multifunctional Yagura
Built on top of strong stone walls, 櫓（やぐら／yagura）served multiple roles and were indispensable parts of a castle’s defensive system. They provided positions for observation and attack while also functioning as storage facilities, reflecting the ingenuity of Japanese castle construction.
The Evolution of Yagura: From Simple Lookout Posts to Fortified Towers
The history of yagura is extremely old, and structures resembling their early forms can even be found in archaeological remains from the Jōmon and Yayoi periods. In illustrated scrolls from the Heian period, yagura often appear as temporary observation and defensive structures used during sieges. The word 櫓 may originally have been written as 矢倉 or 矢蔵, referring either to a storehouse for arrows or an elevated platform from which archers could shoot.
From the late Sengoku period into the Edo period, castle architecture became increasingly complex and refined, and yagura developed from simple wooden structures into permanent buildings. They were constructed on foundation stones, had thick earthen walls for protection against fire and bullets, and were covered with tiled roofs. The widespread use of firearms made it necessary for yagura to become even stronger so that they could withstand more powerful attacks. During the Azuchi–Momoyama period, high stone walls and tile-roofed yagura appeared in large numbers in castles built by daimyō associated with Toyotomi Hideyoshi. Their decorative features also became increasingly elaborate, turning them into part of the visual display of a lord’s authority. After the Battle of Sekigahara, many different forms of yagura were built, particularly in castles across western Japan.
The Functions of Yagura: Multiple Roles in the Castle’s Defensive Network
Yagura served several important roles within a castle:
- 物見（Observation）: From an elevated position, guards could monitor enemy movements and the surrounding area, providing early warning of an approaching attack.
- 防禦・攻擊（Defense and attack）: Built on stone walls or earthen embankments, yagura functioned as firing positions against attacking forces. In addition to ordinary windows, they were usually equipped with small openings such as 矢狭間（arrow slits）and 鉄砲狭間（gun loopholes）, allowing archers and matchlock troops to fire effectively at enemies below.
- 倉庫（Storage）: Yagura were used to store weapons, ammunition, food and other essential supplies. During the peaceful Edo period, as warfare became less frequent, their observation and defensive functions gradually diminished, and many were used primarily as dedicated storage facilities.
- 天守代用櫓（Tenshu-daiyō-yagura）: When a keep was destroyed by fire or other disasters, or in castles where no keep had been built, certain large yagura could effectively take on the role of the keep, serving as the castle’s symbol and command center. Hirosaki Castle’s 御三階櫓 is a famous surviving example.
The Architectural Beauty and Many Types of Yagura
Yagura developed from simple early wooden structures into strong and durable buildings. Their foundations were generally built on stones placed above stone walls or earthen embankments. Their walls were covered with thick layers of earth to improve defensive strength, while their roofs were usually tiled. In appearance, yagura could resemble tenshu and were also divided into 望樓型（watchtower style）and 層塔型（layered-tower style）forms. In the watchtower style, a smaller lookout structure was built above the roof of the lower level. In the layered-tower style, the floor plans of the different levels were relatively similar and stacked vertically. The size of a yagura was usually described using 重, referring to the number of visible roof tiers, and 階, referring to the number of internal floors.
There were many types of yagura, classified according to their shape, number of floors, position and function:
- 平櫓（Hira-yagura）: A yagura with a single roof tier, used mainly for defending the castle walls rather than for observing from a great height.
- 二重櫓（Nijū-yagura）: A yagura with two roof tiers. This was a common standard form during the Edo period and combined observation and defensive functions.
- 三重櫓（Sanjū-yagura）: A yagura with three roof tiers. Its impressive appearance could sometimes rival that of a small keep.
- 多聞櫓（Tamon-yagura）: A long, corridor-like yagura built along stone walls or earthen embankments. It could connect the keep, other yagura or castle gates, creating a continuous defensive line. It is traditionally said to have first been created by Matsunaga Hisahide at Tamon Castle in Yamato Province.
- 隅櫓（Sumi-yagura）: A turret built at the corner of a castle compound, usually with one or two roof tiers, responsible for defending strategically important corners.
- 櫓門（Yagura-mon）: A combined structure in which a yagura was built above a castle gate, serving both as an entrance and as a defensive observation post.
- 渡櫓（Watari-yagura）: A building connecting two yagura, or connecting a keep with a yagura. It is also sometimes regarded as a type of tamon-yagura.
- 付櫓（Tsuke-yagura）: A smaller turret attached to a keep or another large yagura, generally serving as an entrance or as an additional defensive structure.
Yagura were named in many different ways. Their names might come from their direction, such as 巽櫓; a number, such as 一番櫓; their use, such as 太鼓櫓; a place name, such as 伏見櫓; or their distinctive shape, such as 天秤櫓 and 菱櫓. Each yagura carried its own historical memories and tactical significance.
At the Summit of the Castle: The Symbolism and Architectural Secrets of the Magnificent Tenshu
The 天守（てんしゅ／tenshu）is the highest and most visually prominent building in a Japanese castle. It was not only a symbol of the castle lord’s authority and military power, but also a masterpiece of Japanese architectural art.
The Tenshu: The Highest Expression of a Castle Lord’s Power
The tenshu, commonly called a 天守閣, refers to the tallest multi-story structure within a Japanese castle and represents the material expression of the castle lord’s political authority and military prestige. It was usually located at the center of the castle and offered excellent visibility, allowing the lord to survey the surroundings and issue commands. Although the word 天守閣 only became widely used after the Meiji period, the tenshu’s position as the most prominent building in the castle was unquestioned. During the Edo period, the tenshu was rarely used as the lord’s everyday residence. Castle lords usually lived and handled administrative affairs in palace buildings located in the honmaru or ninomaru. During the Sengoku period, however, the tenshu remained important as a final defensive stronghold.
Today, tenshu have become important cultural heritage sites and popular tourist attractions in Japan. Many keeps destroyed during wars were restored or reconstructed after the Second World War. These buildings not only contributed to local tourism, but were also often converted into museums displaying valuable historical materials and artifacts related to the Sengoku period and Japanese castles, allowing modern visitors to gain a deeper understanding of Japanese history and culture.
The Structure and Appearance of Tenshu: From Independent to Coalition-Style Complexes
Tenshu can be classified according to how they are connected to their accompanying buildings:
- 獨立式天守（Independent-style tenshu）: The keep stands alone without any attached structures. This form was more common during the Edo period and symbolized the stable rule of the castle lord during a time of peace. The surviving keeps of Hirosaki Castle and Maruoka Castle are typical examples.
- 複合式天守（Compound-style tenshu）: Smaller attached turrets or tamon-yagura are directly connected to the keep, increasing the complexity of its defenses. The keep of Okayama Castle belongs to this category.
- 連結式天守（Connected-style tenshu）: The main keep is connected to a smaller keep or another yagura by a 渡櫓, a corridor-like connecting turret. Matsumoto Castle is a representative example of this form and is sometimes described more specifically as a connected compound-style tenshu.
- 連立式天守（Coalition-style tenshu complex）: This was the most complex and heavily defended form. A main keep, smaller keeps, intermediate keeps and multiple groups of yagura were linked by several watari-yagura, creating a large defensive complex. Himeji Castle and Matsuyama Castle in Ehime Prefecture are outstanding examples.
In terms of external appearance, tenshu can also be divided into two major types:
- 望樓型天守（Watchtower-style tenshu）: A smaller watchtower was built above the roof of a larger lower structure, usually constructed in the irimoya hip-and-gable style. This form was common from the late Sengoku period through the Azuchi–Momoyama period.
- 層塔型天守（Layered-tower-style tenshu）: Like a five-story Buddhist pagoda, each level followed a consistent architectural style from bottom to top, and the floor plans did not vary greatly in size. This form emerged after the Battle of Sekigahara and became the dominant style during the middle and later Edo period.
Witnesses to History: Japan’s Twelve Original Castle Keeps
Only twelve tenshu built during or before the Edo period have survived intact to the present day. They are known as the 現存十二天守, or the Twelve Original Castle Keeps. These structures survived warfare, natural disasters and the castle abolition policies of the Meiji period. Each carries immense historical significance and represents an invaluable part of Japan’s cultural heritage. Five have been designated National Treasures of Japan, while the remaining seven are designated Important Cultural Properties.
The Five National Treasure Castles:
- 姬路城（Himeji Castle, Hyōgo Prefecture）: Famous for its elegant white exterior and complex coalition-style keep, it is known as the “White Heron Castle” and is also a UNESCO World Heritage Site.
- 松本城（Matsumoto Castle, Nagano Prefecture）: Known for its distinctive black exterior and often called “Crow Castle,” it is a representative example of a connected-style keep.
- 犬山城（Inuyama Castle, Aichi Prefecture）: One of Japan’s oldest surviving castle keeps, distinguished by its watchtower-style architecture.
- 彥根城（Hikone Castle, Shiga Prefecture）: A National Treasure keep known for its refined design and variety of defensive features.
- 松江城（Matsue Castle, Shimane Prefecture）: Known for its black exterior and distinctive watchtower-style keep, it is one of the few Japanese castles where visitors can view the internal supporting structure.
The Seven Important Cultural Property Castles:
- 弘前城（Hirosaki Castle, Aomori Prefecture）
- 丸岡城（Maruoka Castle, Fukui Prefecture）
- 備中松山城（Bitchū Matsuyama Castle, Okayama Prefecture）
- 丸龜城（Marugame Castle, Kagawa Prefecture）
- 伊予松山城（Matsuyama Castle, Ehime Prefecture）
- 宇和島城（Uwajima Castle, Ehime Prefecture）
- 高知城（Kōchi Castle, Kōchi Prefecture）
Each of the Twelve Original Castle Keeps has its own distinctive history, architectural style and defensive features waiting to be explored and appreciated. They are living witnesses to Japanese castle culture and works of art that have endured across the centuries.
Stone Walls, Turrets and Keeps: The Perfect Symphony of Japanese Castle Architecture
Stone walls, turrets and keeps were never independent structures within Japanese castle architecture. They were closely connected and mutually dependent. Together, they formed a complex and effective defensive system that combined military strategy, political authority and aesthetics.
Strong stone walls served as the foundation of the entire castle. They greatly strengthened its defenses while providing a stable base for the buildings above. Yagura were strategically positioned at important points along the stone walls, functioning as observation posts, firing positions and storage facilities, while preventing enemies from climbing or approaching the castle walls. At the center of the castle, the tenshu stood behind multiple layers of protection provided by the stone walls and yagura, allowing it to fulfil its role as both a symbol of power and a final defensive stronghold.
For example, the attached turrets connected to a tenshu and the connecting turrets linking different yagura or castle gates clearly demonstrate the close relationships between these structures. They were not individual buildings operating separately, but essential parts of a coordinated and complete defensive system. From the turmoil of the Sengoku period to the peace of the Edo period, the construction techniques and design concepts of stone walls, turrets and keeps continued to develop, eventually creating a uniquely Japanese castle culture that displayed exceptional knowledge and creativity.
When Visiting a Castle, Look at the Stone Walls First, Then the Turrets, and Finally the Keep
Japan’s stone walls, turrets and keeps are not only remarkable architectural achievements, but also lasting records of Japanese history and culture. Beginning as relatively simple fortifications, they developed through periods of warfare and peace into magnificent castle complexes that combined strong defenses, sophisticated craftsmanship and an imposing visual presence.
Every time you visit an old castle, touch its weathered stone walls, look up at its towering keep or imagine the guards once stationed inside its turrets, you can sense the passion and ingenuity of Japan’s warrior era. These valuable cultural heritage sites are not only windows into Japanese history, but also excellent places for modern visitors to appreciate architectural beauty and cultural traditions. The next time you visit a Japanese castle, slow down and take the time to observe the strength of the stone walls, the ingenuity of the turrets and the grandeur of the keep. You may find yourself gaining a much deeper understanding of Japanese history and culture.
Frequently Asked Questions: Stone Walls, Turrets and Keeps Explained
Q1: What are stone walls, turrets and keeps?
A: Stone walls are the stone foundations and defensive walls of a castle, providing structural support and protection. Turrets are towers positioned at important locations and used for observation, shooting and storage. The keep is the tallest symbolic building in the castle and served as both an observation and command point and, in some cases, a final defensive stronghold.
Q2: Why do Japanese castle stone walls often have beautiful curves?
A: Japanese castle walls often feature an inward-curving profile. In addition to their visual appeal, these curves also served structural and defensive purposes. Combined with carefully arranged stones, drainage systems and internal backing stones, they helped improve the overall stability and durability of the walls.
Q3: What is the difference between nozura-zumi, uchikomi-hagi and kirikomi-hagi?
A: The main difference is the precision with which the stones were processed and fitted. Nozura-zumi uses natural stones and leaves larger gaps. Uchikomi-hagi uses stones with roughly shaped edges, reducing the spaces between them. Kirikomi-hagi uses precisely cut stones that fit tightly together.
Q4: Were turrets used only for defense?
A: No. Turrets were also used to store weapons, food and other supplies. In castles without a keep, or where the keep had been destroyed, certain large turrets could also serve as the castle’s main symbolic and command structure, functioning as substitute keeps.
Q5: Why was the keep not the castle lord’s main residence?
A: During most periods, the castle lord lived and conducted administrative affairs in palace buildings located in the honmaru or ninomaru. The keep was used more as a symbol of authority, a wartime stronghold and a location for observation and command.
Q6: What are the Twelve Original Castle Keeps, and which are National Treasures?
A: The Twelve Original Castle Keeps are the twelve keeps built during or before the Edo period that survive to the present day. Five are designated National Treasures: Himeji Castle, Matsumoto Castle, Inuyama Castle, Hikone Castle and Matsue Castle. The remaining seven are designated Important Cultural Properties.