The Church of Saint Paraskevi is a partially preserved medieval Eastern Orthodox church in Nesebar, a town on the Black Sea coast of Burgas Province in eastern Bulgaria. It was most likely built in the 13th or 14th century and forms part of the Ancient Nesebar UNESCO World Heritage Site. The Church of Saint Paraskevi features a single nave and a pentagonal apse as well as rich exterior decoration. Its dome and the belfry surmounting the narthex have not been preserved today, and it is unknown which of the three saints named Paraskevi it was dedicated to.
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.