Shiryōkaku (四稜郭) (literally, 'four-point fort') is a fort in the city of Hakodate. 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.
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.
References:The ancient Argos Theater was built in 320 BC. and is located in Argos, Greece against Larissa Hill. Nearby from this site is Agora, Roman Odeon, and the Baths of Argos. The theater is one of the largest architectural developments in Greece and was renovated in ca 120 AD.
The Hellenistic theater at Argos is cut into the hillside of the Larisa, with 90 steps up a steep incline, forming a narrow rectilinear cavea. Among the largest theaters in Greece, it held about 20,000 spectators and is divided by two landings into three horizontal sections. Staircases further divide the cavea into four cunei, corresponding to the tribes of Argos A high wall was erected to prevent unauthorized access into the theatron and may have helped the acoustics, but it is said the sound quality is still very good today.
Around 120 CE, both theaters were renovated in the Roman style.