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 Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.