The Cathedral Basilica of the Holy Cross (Bazylika Katedralna Podwyższenia Krzyża Świętego) was built in the 15th century on the site where before there was a structure of the 11th and 13th centuries. It was rebuilt several times. With towers with a height of 73 meters is the tallest structure in the city. In the temple there is a painting of the Virgin of Opole, brought there permanently in 1702.
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.