The Gate of Spalen (Spalentor) is a former city gate in the ancient city walls of Basel. One of the three remaining gateways, it is regarded as one of the most beautiful gates of Switzerland.
In October 1356, a major earthquake destroyed the old Basel. Then local people surrounded their newly built city with a high city wall and a moat in front of it. The ring wall had over 40 towers and seven of them were gate towers like the Spalentor (completed in 1473-74).
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.