Coetan Arthur dolmen, also known as Arthur's Quoit (not to be confused with Carreg Coetan Arthur, near Newport) is the remains of a Neolithic burial chamber (also known as a quoit). It dates from around 3000 BCE. The site, situated on the hillside close to St Davids Head in Pembrokeshire, Wales, is the collapsed chamber of what is presumed to be a passage grave which also has a round barrow. The massive capstone measures approximately 6 metres by 2.5 metres and is supported on one side by an orthostat approximately 1.5 metres in height.
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.