The Martinikerk (Martin's church) is the oldest church in Groningen. The church and its associated tower (the Martinitoren) are named after Saint Martin of Tours (316–397), the patron saint of the Bishopric of Utrecht to which Groningen belonged. The church was a cathedral for a short period during the first bishopric of Groningen (1559–1594).
The origins of the Martinikerk are a cruciform church built in the 13th century, which was extended in the 15th and 16th centuries. It contains several 16th century tombs and Wessel Gansfort's 18th century tomb. Much of the wall and roof paintwork has been preserved. Of particular note is a 16th-century depiction of the life of Jesus Christ.
The tower was built from 1469 till 1482, with later additions. Citizens of Groningen often refer to the tower as d'Olle Grieze (Old Grey One). The original 13th century tower was destroyed by lightning and a new tower was built in the 15th century, also destroyed by lightning.
References:Since I can’t be there, maybe someone would be interested in taking a video of where the Organ is situated; then kindly uploading it to YouTube, for instance.
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.