St. Peter's Square (Piazza San Pietro) is a large plaza located directly in front of St. Peter's Basilica in the Vatican City, the papal enclave inside Rome, directly west of the neighbourhood or rione of Borgo.
At the centre of the square is an ancient Egyptian obelisk, erected at the current site in 1586. It was made of red granite and is 25.5 metres tall. The obelisk was originally erected at Heliopolis, Egypt, by an unknown pharaoh.
Gian Lorenzo Bernini designed the square almost 100 years later, including the massive Tuscan colonnades, four columns deep. A granite fountain constructed by Bernini in 1675 matches another fountain designed by Carlo Maderno in 1613.
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.