The Great Construction Project in the Period of Reiwa: The Fukuyama Castle Coming Back to Life


To commemorate the 400th anniversary of the birth of the castle, restoration was conducted of the iron plates, which are arguably the only ones of their kind in Japan, on the north end of the castle keep, along with the window shapes, sama gun slits, and other parts of the castle, to make it look as it did in the days from the end of the Tokugawa shogunate to the abandonment of the castle.

*The works were conducted according to the architectural constraints on the current castle keep, which is made of steel frames and reinforced concrete.


1. Examination of the north-end iron plates

The iron plates of the north end had a dual purpose:
(1) They were designed to protect against rain and winds.
(2) Since the tower was not at the center but nearer to the north of the castle, the plates were intended to defend the tower from direct attacks from outside.

Of all the documents recording the iron plates, the oldest is Bingo Fukuyama no Oboegaki (A Memorandum of Fukuyama, Bingo), 1698, which is a document formerly owned by the Ikeda family and now stored at the Okayama University Library. This record confirms that when the Mizuno family was the lord of the domain, the iron plates were attached to the tower. In connection with their restoration, the designers examined the documents specifying the north-end iron plates and the photos taken before WWII and used the cases similar to the conditions of the Fukuyama Castle as supplementary information.


2. North-end iron plates conjectured based on our investigation

Wooden plates were presumably attached there. And on top of them, iron plates shaped like small tags were probably riveted down so as to make them overlap each other slightly from east to west.

The plates were piled one on top of another–a technique called hagasane.
The general coloring of the plates was between black and gray, partially with red rust.The blackening probably stems from a former rustproofing agent deteriorated or coming off, or from some iron itself having formed a layer of black rust covering the surface.

The plates were attached, beginning with the left ones and, from then on, sequentially. One plate was fixed with nine rivets at the left end, eight in the middle.
The rivet heads were arranged obliquely. That was what characterized the iron plates on the north end of the tower of the Fukuyama Castle.

The plate system consisted of rectangular iron plates piled one on top of another, 113 mm wide and 1,302 mm long.
The plates, with consideration given to the manufacturing technique and lateral overlap, seem to have been a little thick in the middle (1.5 to 2.0 mm) and thin at the edges (0.8 to 1.1 mm).


3. Restored based on the inspection, according to the basic principle of works with attention to safety and reproducibility

(1) Material and iron plate specifications
The plates are of iron (Galvalume steel), basically 1,300 mm long, 114 mm wide, and 0.6 mm thick. About 2,000 of them were attached.

(2) A texture that reproduces the iron plates of the time
The original texture of the iron plates with dips and bumps and with some unevenness has been reproduced by iron aging paint.

(3) Hagasane, which reproduces plates as piled one on top of another
The iron plates of the time were fixed by piling them one on top of another from bottom to top. So the bottom edges of the plates have been piled one on top of another and slightly floated to reproduce the hagasane technique.

(4) Rivets reproduced based on the real things
We conducted 3D scans of Sujigane-Gomon Gate and other modern castles (the Himeji Castle and the Nagoya Castle) to reproduce the rivets that retained the iron plates in those days.


4. Other works

Based on old photos, the top layer window has been restored to its former layout, consisting of kato mado (arched window), sliding doors, and nurigome (an earthen-walled compartment).

The sama gun slits were restored as regular hexagons on the second layer of the tower (one on the east, one on the west, two on the south), the third layer (one on the south), and the fourth layer (one on the east and another on the west), measuring about 260 mm at their largest width, with the external walls of the bargeboards dented. These regularly-hexagonal gun slits are of a rare shape.

Reshaping of the windows on the second floor of the south and the north wings

Painting was performed anew on the nageshi, koran, and similar parts on the top floor, along with the windows and vertical lattices on the first to the fourth floors.


Iron plates as restored just like on the Fukuyama Castle in the old days

Based on some old photos of the Fukuyama Castle and on the actual iron plates and nails donated to Fukuyama City, Hiroshima Prefecture, the Tomo-no-ura History Museum, Fukuyama City, and the ironworks that has inherited the traditional art of blacksmiths for archer’s wrist protector have together restored the iron plates and rivets (nails). The iron plates, about 1,300 mm long, about 114 mm wide, and about 3 mm thick, have been made to present their textures by heating and striking the iron surfaces. The rivets, about 50 mm long, have been made by heating, striking, and forming masses of iron a number of times. These rivets have then been used to fix the restored iron plates to reproduce the lateral hagasane technique.