St. Hallvard's Cathedral (Hallvardskatedralen), the former Oslo Cathedral, was the earliest cathedral in Oslo. The cathedral was built at the height of the Old Town market square Oslo during the early 12th century, and was used as a church until about 1655. Besides being the bishop's seat and religious center of eastern Norway for about 500 years, the cathedral was the coronation church, royal wedding church, chapel royal, and one of Scandinavia's most visited place of pilgrimage. St. Hallvard cemetery is located mainly south of the cathedral. It was the honorary cemetery in Oslo and eastern Norway from around 1130 to 1639. Here the bishops, chiefs and other prominent men and women were buried. The most prominent was interred in the church along with the kings.
Today the cathedral is in ruins. The main body in the ruins park (Memorial Park), the southern part under a concrete cap - and the concrete lid of the street of Bispegata. Towards the end of the 19th century were Bispegata extended in an easterly direction, over the cathedral site. It has been put in place to remove Bispegata's eastern part, as a result of the completion of the Ekeberg Tunnel and the modified veian resort in the lower Lodalen. In that case, the ruins of St. Hallvard Cemetery exposed, and the Medieval city triangular marketplace, Oslo squares, re-established west of St. Hallvard Cemetery. Neighboring the Cathedral was the smaller Church of the Cross.
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.