There are two ancient hill forts in Porvoo, so-called small and big one. There is burial ground in a small hill from the Roman Iron Age (0-400 AD). The items found in excavations reveal that Porvoo river has been a remarkable trading centre already in prehistoric times and local people has had connections to Estonia and Latvia.
The bigger hill fort is one of the largest in Finland. It was used for defensive purposes already in the Viking Age (800-900 AD), but the fortifications date from the late 14th century. Today remains of double walls and dry moat are visible and restored.References:
Goryōkaku (五稜郭) (literally, 'five-point fort') is a star fort in the Japanese city of Hakodate on the island of Hokkaido. The fortress was completed in 1866. It was the main fortress of the short-lived Republic of Ezo.
Goryōkaku was designed in 1855 by Takeda Ayasaburō and Jules Brunet. Their plans was based on the work of the French architect Vauban. The fortress was completed in 1866, two years before the collapse of the Tokugawa Shogunate. It is shaped like a five-pointed star. This allowed for greater numbers of gun emplacements on its walls than a traditional Japanese fortress, and reduced the number of blind spots where a cannon could not fire.
The fort was built by the Tokugawa shogunate to protect the Tsugaru Strait against a possible invasion by the Meiji government.
Goryōkaku is famous as the site of the last battle of the Boshin War.