The Ring Of Brodgar Stone Circle And Henge, which is part of The Heart of Neolithic Orkney World Heritage Site, is a spectacular stone circle. The ring is surrounded by a large circular ditch or henge. The truly circular layout of the ring is an unusual attribute that singles it out as one of the largest and finest stone circles in the British Isles. The Ring of Brodgar (alternative spelling Brogar) comprises a massive ceremonial enclosure and stone circle probably dating from between 2500 and 2000 BC. Around it are at least 13 prehistoric burial mounds and a stone setting (2500-1500 BC). The erecting of the stones, along with the massive rock cut ditch was an activity that required considerable manpower and organisation.
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.