First built in 1248 as a Romanesque basilica with a nave and two aisles, the cathedral gained its current appearance in the 15th century as a Gothic structure, though the Baroque chapels date from the 16th and 18th centuries. Inside, one is treated to the sight of a lavishly adorned altar, which lights up the place all on its own.
The 57 metre high classicist designed bell tower dates back to the end of the 18th century as the primarily 76-metre high bell tower built by Pavel Porta in the year 1623 was struck by lightening.
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.