Shiryōkaku

Shiryōkaku (四稜郭) is a fort in the city of Hakodate in southern Hokkaidō, Japan. It was constructed in April 1869, during the Battle of Hakodate, three kilometres to the northeast of Goryōkaku by two hundred soldiers of the former Tokugawa shogunate and a hundred local villagers, likely under the direction of Ōtori Keisuke. Goryōkaku is a star fort with five triangular bastions; Shiryōkaku instead has four, and is sometimes known as the "butterfly fort" as opposed to the "star fort".

The fort covers an area of 21,500 m2, stretching approximately a hundred metres east to west and seventy metres north to south; the earthworks rise to a height of 3 m with a width of 5.4 m; they are surrounded by a dry moat 0.9 m deep and 2.7 m wide; the entrance is to the southwest.

Shiryōkaku fell to government forces within a few hours on 11 May 1869.

In 1934 the area was designated an Historic Site. Repairs were carried out from 1970-2 and again in 1990.