The Gothic collegiate complex built from 1357–1389, with a splendid church, on which Pope John Paul II conferred the title of minor basilica (1989). Undoubtedly, one of the biggest tourist attractions beside the magnificent interior and furnishings of the church is the organ with 49 tones and 3522 pipes. The former capitulary library houses a parish museum, which is open to visitors. It contains the remains of the old outfit of the collegiate. Unfortunately, the rich vault as well as the collection of books and manuscripts largely scattered after World War II.
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.