Collegiate Church of the Holy Cross and St. Bartholomew is one of Ostrów Tumski's most beautiful and iconic structures, thanks to a 70m steeple and impressive entry staircase, this curious sanctuary is actually two churches in one. Split over two levels, the building comprises the shorter windows of the Church of St. Bartholomew beneath the soaring windows of the upper level Church of the Holy Cross. The first two-storey church in Silesia, and one of only a few in all of Europe, the church was completed in 1295 as an act of reconciliation ending a long dispute between Duke Henry IV and Bishop Thomas II. For centuries the sarcophagus of Henry IV was housed in the upper Church of the Holy Cross, however today it can be seen on display in the National Museum. Standing outside the church is a large sculpture of John of Nepomuk dating from 1732.
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.