Middelgrundsfortet is a sea fort located in the Øresund between Copenhagen and Malmö. It was constructed 1890–1894 as a part of Copenhagen's sea-fortifications, partly from material excavated from Frihavnen. It is one of three artificial islands that were created to defend the entrance to Copenhagen's harbor (the other two are Flakfortet and Trekroner Fort).
Middelgrundsfortet was the largest sea fortress in the world, and is still the largest man-made island without abutment, with an area, including wave breakers, of approximately 70 000 m²; the buildings total approximately 15 000 m². A HAWK battery was placed on the island. Until 1984 the fortress was a military area; in 2002 it was sold to a private investor. Ferries connect Middelgrundsfortet with Langelinie, Copenhagen.
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.