Torsburgen was the largest ancient fortress in Northern Europe. It was originally constructed at the beginning of the 1st century AD. It was reinforced during the 4th century and used until c. 1100 AD. A timber-laced stone rampart encircles an area of 12 hectares. Scholars estimate that nearly 1000 soldiers would have been needed to defend it and it could have been providing refuge to the entire population of Gotland that is calculated to be between 6,000 and 10,000 in the early medieval period.
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.