Crucuno dolmen is one of the most well known dolmens in the Brittany. The rectangular chamber is about 4 metres by 3.5 metres, covered by a single massive capstone which measures over 7 metres in length, perched on top of 9 support stones, with easily enough room to stand upright inside. The enormous capstone is 7.6 metres in length and weighs about 40 tons. Unfortunately, a century or so ago, a house was built right next to it, and this has destroyed all but the last pair of entrance passageway uprights and their capstone. This passageway was recorded in the last century as being 20-25 metres in length, leading away towards the southeast.
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.