Dolmen de la Madeleine is an isolated dolmen located in a private field on the outskirts of the town of Gennes. It was probably built between 5 000-2 000 BC. There are a number of these sites in the area - but this one is said to be the largest. Like many of the larger dolmens, it has subsequently been re-used, in this case to house a bread oven. Although the bread oven is no longer in use as the dolmen is now a classified national monument, you can still see the remains of the oven.
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.