Pentre Ifan contains and gives its name to the largest and best preserved neolithic dolmen in Wales. As it now stands, the Pentre Ifan Dolmen is a collection of seven principal stones. The largest is the huge capstone, 5 m long, 2.4 m wide and 0.9 m thick. It is estimated to weigh 16 tonnes and rests on the tips of three other stones, some 2.5 m off the ground. There are six upright stones, three of which support the capstone. Of the remaining three, two portal stones form an entrance and the third, at an angle, appears to block the doorway.
The dolmen dates from around 3500 BC, and has traditionally been identified as a communal burial. Under this theory the existing stones formed the portal and main chamber of the tomb, which would originally have been covered by a large mound of stones about 30 m long and 17 m wide. Some of the kerbstones, marking the edge of the mound, have been identified during excavations. The stone chamber was at the southern end of the long mound, which stretched off to the north. Very little of the material that formed the mound remains. Some of the stones have been scattered, but at least seven are in their original position. An elaborate entrance façade surrounding the portal, which may have been a later addition, was built with carefully constructed dry stone walling. Individual burials are thought to have been made within the stone chamber, which would be re-used many times. No traces of bones were found in the tomb, raising the possibility that they were subsequently transferred elsewhere.
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.