La Hougue des Geonnais is a passage chamber from the Neolithic age. It is today largely ruined by quarrying prior to the initial excavation in 1929. There is no capstone anymore. At that time the chamber was found to have a paving of pebbles and a large quantity of pottery fragments were disguarded in the spoil heaps. Excavation between 1985 & 1990 revealed a chamber that was probably constructed in two phases. A D shaped chamber being built first and then later extended to its current form. In 1990 some of the main chamber's missing uprights were replaced by dated, modern grantite blocks. A vast number of finds included pottery, flint scrapers, arrowheads and broken querns.
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.