The Church of the Holy Archangels Michael and Gabriel in Nesebar, Bulgaria, is a partially preserved medieval Eastern Orthodox church, built in the 13th or 14th century. As part of the Ancient Nesebar UNESCO World Heritage Site, it stands in the old town and has been under state protection since 1927. The church, with a cross-in-square plan, features three apses and a large narthex. Despite partial preservation, it remains culturally significant, boasting opulent external decoration characteristic of Nesebar's medieval religious architecture. The architectural style, opus mixtum, incorporates alternating rows of brickwork and stones in a chequered pattern.
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.