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A Japanese Castle 

 by Stephen Francis Wyley

Drawings by Steven Lowe


A castle is a fortified building or set of fortified buildings used to provide both active and passive defence, as well as a residence for the castle's occupants, usually the castle's lord and household. A ‘shiro’ is the Japanese equivalent of a European castle, a shiro may appear to Europeans eyes as some thing far less robust to what they would be used to in their homelands but a shiro fulfilled the same functions as their European counter parts.

The aim of this essay is to examine a shiro’s design features and their functions.

The building we know today as a shiro (or ) was developed in the short period between the last part of the fifteenth century and the first part of the seventeenth century. The major elements of the design and technology were borrowed from both religious and residential architecture of the period.

Oda Nobunaga (1534-82) built Azuchi - Jõ between 1576 and 1579, it marked his rise in the struggle for control of Japan in the 16th century. Many other lords followed his lead, each lord needed a strong defensive base to support his aspirations. But once the forces under Tokugawa Ieyasu (1542-1616) finally defeated those of Toyotomi in 1615 the age of the shiro was at an end. In the sixth month of 1615 a shogunal edict was issued ordering the destruction of all regional fortifications except for the actual residences of the local lord. A document from the period stated that four hundred castles and lesser fortifications were dismantled in only a few days.

Strategic Placement

Shiro’s were built on strategic sites to take advantage of the position itself (eg. height advantage, difficult access for an aggressor, water and supply availability, ease of communication and control of transport routes). The three main situations shiro’s were built were;

1) on the top of a hill (yamajiro);

2) and on a hill surrounded by a flat plain (hirayamajiro);

3) on a flat plain (hirajiro).

A yamajiro (J. mountain castle) was usually built on a mountain top or some other elevated position, constructed using walls of rocks and earth to reinforce the natural defences of the site, a moat was optional. This form of castle was the favoured form prior to the latter half of the 16th century, were the lessening of civil strife began to show an effect.

A hirayamajiro (J. flatland hill castle) was constructed on a hill on a plain, thus taking the positional advantage of the surrounding area.

A hirajiro (J. flatland castle) was developed after the necessity of the yamajiro fortification declined with the cessation of civil war in the 17th century. These castles were built on the plains and served as administration centres of the surrounding area.

Fortified compounds

Honmaru and Ninomaru of Osaka-jo.
Figure1. Honmaru and ninomaru of Osaka - jõ

Most shiro’s consisted of a either one or more joined compounds or 'kuruwa', these were the:

1) honmaru,

2) ninomaru,

3) and sannomaru.

The honmaru (J. main circle) (see figure 1) was the main or inner fortified compound of a shiro. The ninomaru (J. second circle) was the second defensive compound of a shiro, which either surrounded or was adjacent to the honmaru. The sannomaru was the tertiary defensive courtyard of a shiro, depending on the design, the sannomaru either, surrounded the ninomaru or was sited adjacent to it.

A dôshinén was one of the three major types of shiro which date from around 1600 A.D. A dôshinén was constructed using a plan of three fortified compounds arranged in concentric pattern; the honmaru in the centre was surrounded by the ninomaru which in turn was surrounded by the sannomaru, variations on this occurred depending on the site.

The renketsukei was another one of the three major types of shiro which dating from around 1600 AD. Arranging the honmaru, the ninomaru and the sannomaru in series along an axis, and connecting them by gateways formed a renketsukei.

The teikakukei is the final one of the three major types of shiro which dating from around 1600 AD. The teikakukei consisted of two defensive compounds; the inner or honmaru was set to one side of the encircling secondary compound or ninomaru. This positioning of the homnaru was to remove it from the most likely line of assault, thus gaining extra protection.

Basic Design

The basic design of a shiro consists four main elements:

1) Moats or hori;

2) Walls or ishigaki;

3) Gates or mon;

4) and Towers or tenshu.

Ishigaki and Dobei (walls)

Yagura a top ishigaki
Figure 2. Yagura a top ishigaki.

An ishigaki or dry stone wall (see figure 2) was used in the construction of the main walls of a shiro. The ishigaki was introduced into Japanese military architecture because of the increase in the frequency of conflict and earthworks were no longer a form of effective defence. The technique of construction involved embedding stones into an earthen embankment and locking them in place with smaller stones. This allowed the whole wall to shake and thus dissipate the effect of earthquakes, which are a normal occurrence for the country. The ishigaki were used as a foundation for such structures as; tenshus, corner towers, parapets and connecting towers.

A dobei was a wall made by daubing clay over a reed or bamboo framework and topped by a small tiled roof. This type of wall were used in two different parts of a shiro:

they were built along the top of the ishigaki (or the main walls) linking the corner and connecting towers, providing protection to the defenders within;

and the dobei were also raised on both sides of the castles major ways, effectively screening the rest of the compounds from enemy eyes, and they formed a maze which hindered the enemy greatly if the gained entry.

Mon (gates)

Yagura mon and Korai mon
Figure 3. Yagura mon centre and kôrai mon on left.

A watari yagura mon was the largest kind of gateway used in a shiro, which consisted two story timber frame structure, where the lower story incorporated the entrance, and the upper story formed the connecting tower (from were the gateway derives its name). The style of the connecting tower is typical of a yagura (see figures 2 and 3) but the lower story's timber is left unplastered, and the actual gate and surrounding timbers were often covered with strips or sheets of iron which improved their protection against battering and firing.

The kôrai mon (see figure 3) was the smaller initial gate of a masugata mon or barbican gatehouse complex of a shiro, consisting of a three roofed structure (a central roof was flanked by another two roofs). This gate restricted access to the courtyard beyond, and if the enemy did gain entry to the courtyard they would be confined within that space and would be exposed to the fire of the defenders.

Tenshus (towers)

 Figure 4. Tenshu.

The main tower of a shiro, constructed mainly of timber on a base consisting of ishigaki or earth revetted with dry stone walling, serving a number of purposes such as; ceremonial, residential and military. The early tenshu were simple residential buildings with belvederes perched on their roof tops, later they developed into the larger multi-levelled towers.

As tenshu (see figure 4) developed various types evolved, they were:

the boroshiki tenshu, which was the earliest form of tenshu, consisting of a multi-storied timber, framed tower with a belvedere or observation tower set on top of the roof ridge;

the renketsushiki tenshu, which was the most ornate and complex type of tenshu, the tenshu was
connected to smaller towers by parapets a the corners of the rectangular stone base;

the renritsushiki tenshu which was attached to a secondary tower by a connecting parapet;

and finally the teiritsushiki tenshu, which consisted a principal tower, attached directly to a secondary
tower, was also known as a fukugôshiki tenshu.

Other design features

Various other features of a shiro went towards making it very distinctive, if not more defensive in nature.


Since most of the buildings of a shiro were mainly constructed of wood there was the necessity of reducing the risk of fire. This was accomplished by the technique of covering the walls and timbers with a thick layers of plaster, which is known as 'dôzo-zukuri'. The plastering was used as a protection against domestic fires as well as those caused by the incendiary missiles of an enemy.

Ishi-otoshi mado

Ishi-otoshi mado
Figure 5. Ishi-otoshi mado, stone dropping window.

A ishi-otoshi mado (J. stone dropping window) (see figure 5) was structure which was used for the vertical defence of the walls of a shiro, consisting of a section of the wooden or plastered wall of a; tenshu, tower, connecting tower or other structures, which was built out over the stone walls at strategic locations. The structures enabled the defenders to shoot arrows as well as throw stones at attackers attempting to scale the walls. The aperture could be closed for protection if necessary by a panel of thick wood that was strengthened by iron bars.


A teppôsama or musket port was set into the plastered wall or tower of a shiro. In section a port was funnel shaped, the larger part on the inside gave a greater field of fire to the defenders, while the narrower aperture on the exterior provided protection to the defenders from incoming fire. The teppôsama came in a number of shapes; rectangular, triangular and circular. The ports of the plastered walls on the ishigaki were left open while those of a wall tower were often provided with shutters, since they were put to other uses other than defence (eg. storehouses or residences).


Shiro's were built to provide a logistics base from which a lord could use to facilitate his campaign. Without a secure site for storage of supplies and defence in case of an attack the lord could never fulfil his grand designs.

The architectural design of a shiro utilised the materials, principles and design features already used for domestic and religious buildings. With the addition of a few defensive design features the shiro became the architectural and historical monuments of the period.

Only a few extant castles survive to this day out of the hundreds that were built in a period of strife. The is due to two major factors: 1) the shogunal edict of 1615; and 2) the nature of the materials used in their construction.


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Castles of Japan

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 Site O is a group of people from around the world that share an interest in fortifications and artillery. Some are authors on the subject, some are connected with Universities and teach it and others are simply fascinated with it.

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Anglo-Saxon Burhs
Bibliography of Military Architecture
David's Tower, Jerusalem
Drawings of Aspects of Military Architecture
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Siege Warfare, The Art of Offence and Defence
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What is a Castle?

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