St. John's Church was built in the 13th century, probably between 1234-1297. It was originally home of the Dominican monks, but over the centuries fell into the possession of the Lutherans. It has also served as an arsenal for the city.
The most notable features of this unheralded church are the impressive 15th century sculptures of St. Peter and St. Paul which adorn the the 18th century altar. According the legend two monks who were bricked to the southern wall during the construction. They spent all their life long and were fed trough a window from the outside.
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.