The Callanish VIII stone setting is one of many megalithic structures around the better-known (and larger) Callanish Stones (I) on the west coast of the isle of Lewis. This is a very unusual (and possibly unique) setting, with a semicircle of four large stones on the edge of a cliff on the south of the island of Great Bernera and looking across a narrow strait to Lewis. There is no evidence that the cliff has collapsed here and destroyed half of a complete circle - it would appear that a semicircle was the original intention. The tallest stone is nearly three metres high and the cliff-edge axis of the circle gives a diameter of about 20 metres.
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.