Tatsuoka Castle

Overview

Tatsuoka Castle (龍岡城, Tatsuoka-jō) is a pentagonal star fort in what is now the city of Saku, in Nagano prefecture. It was built in 1867, the third year of the Keiō era (慶応, Keiō), in the final months of the Edo period (1603–1868). It served as the principal fortress of Tatsuoka Domain, which was ruled by the Ogyū-Matsudaira clan.

The castle is one of only two star fortresses ever built in Japan. The other is Goryōkaku (五稜郭, Goryōkaku) in Hakodate, on the northern island of Hokkaidō. Both were designed with angled, projecting bastions so that defenders could fire along the face of every wall, eliminating the blind spots that a rectangular plan left at its corners. Tatsuoka is therefore often called a "second Goryōkaku", though it is considerably smaller.

The castle ruins have been designated a National Historic Site since 1934.

History

Tatsuoka Castle was begun in 1867, the same year as Goryōkaku's completion, and it belongs to the last, anxious decade of the Tokugawa order. The domain of Tatsuoka was a small one, and the decision to build in the new Western-influenced style reflected a wider turn among Japanese lords toward artillery-era fortification. The pentagonal plan, with five bastions and a perimeter of earthen ramparts and moats, was intended to resist cannon fire rather than the arrows and matchlocks that older castles had been designed against.

The castle was the seat of the Ogyū-Matsudaira, a branch of the Matsudaira family. Construction was still incomplete when the Tokugawa shogunate fell in 1868 and the Meiji Restoration began. The new government abolished the domains in 1871, and Tatsuoka Domain ceased to exist as a political unit. The castle, never fully finished, was dismantled in the years that followed, and much of its stone was carried away for other building work.

What survived was the outline: the moats, the earthen walls, and the pentagonal shape of the enclosure. The site's designation as a National Historic Site in 1934 recognised the rarity of that plan.

What Stands There Today

No keep or main building survives at Tatsuoka. The visitor sees the earthworks and the water defences — the moats and the raised ramparts that trace the five-pointed star. The scale is intimate compared with Goryōkaku, and the site sits among fields and houses on the edge of Saku.

A small structure associated with the castle, sometimes described as a remaining gate or guardhouse, is among the few built elements that survive, and the grounds are laid out as a public park. Because the plan is best understood from above, the pentagonal shape is easiest to appreciate from a high vantage point or from a map; at ground level the angled walls read as a series of grassy banks and ditches.

The Name in Japanese

The castle's name is written 龍岡城. Its kana reading is たつおかじょう, and its romaji is Tatsuoka-jō.

Breaking it down character by character:

• 龍 — read たつ (tatsu) in this name. It means "dragon". This is the older, more elaborate form of the character; the simplified form 竜 is also used in Japanese, but the castle's name uses 龍.
• 岡 — read おか (oka). It means "hill" or "ridge" — a raised, rounded piece of ground. Together, 龍岡 (Tatsuoka) is a place name meaning roughly "dragon hill".
• 城 — read じょう (jō) here. It means "castle". When 城 stands alone as a common noun it is read しろ (shiro); in compound names it shifts to jō, as in 龍岡城, 五稜郭's neighbour 箱館城, or the many castles ending in -jō across Japan.

The final -jō is the standard suffix for a Japanese castle name, so a reader who knows only 城 can recognise the last element of hundreds of castle names. The first two characters, 龍岡, are the domain's name, not a description of the building — the castle is "the castle of Tatsuoka", not "the dragon-hill castle" in any literal sense, though the place name itself carries that meaning.

Note the reading shift: たつおか + じょう, with no sound change at the join. Compare this with names where the suffix alters the preceding syllable.

Visiting and Context

Tatsuoka Castle lies in Saku, in eastern Nagano prefecture, at coordinates roughly 36.20° north, 138.50° east. The site is a public park and can be walked freely; the moats and ramparts are the principal things to see.

For readers of Japanese, the castle is a useful case study in how Japanese names work. The same two characters, 龍岡, name both the domain and the place, and the suffix 城 (-じょう) marks the fortress. The name also illustrates the gap between the on-reading and kun-reading of a character: 城 is shiro alone and jō in compounds, a pattern that recurs throughout Japanese place names and is worth learning early.

Tatsuoka is best understood alongside Goryōkaku in Hakodate. The two are the only star forts in Japan, both built in the 1860s, and both shaped by the same late-Edo awareness that warfare had changed. Goryōkaku is the larger and more famous; Tatsuoka is the quieter, smaller sibling, its earthworks still legible in the fields of Saku.