If you look at this picture and the next one you should be able to see that this fort has a star shape. The Tokugawa shogunate began construction of this castle in 1857 and completed it in 1864. This was the first Western (specifically, Vauban) style fortress in Japan. This style was also popular in Europe at the time for it's ability to withstand damage from modern weapons.

After Japan was forced to open up trading with other countries by the US, the Tokugawa Shogunate opened ports in Hakodate and Shimoda. This fort at Hakodate was designed to defend the city from any Northern threats. Upon completion a government office was established inside which controlled all of Hokkaido.

During the Boshin War (1867-1869) rebel Shogunate forces battled with the Imperial forces after the return of power to the Emperor. The Shogunate forces eventually retreated to Hakodate where they took control of Goryokaku and the Hakodate War began. A year later the last of the rebels surrendered to Imperial forces, thus concluding the last remnant of Feudal Japan.