Since the 14th century craftmen’s guilds were significant brotherhoods who drove interests of their members. The big guild of Tallinn was an union of wealthy merchants. Their base was the Great Guild Hall in downtown, opposite the church of Holy Spirit. The building itself was built in 1407-1410 and is a well-preserved sample of Medieval construction.
Today the Great Guild Hall houses a museum presenting Estonia's history from prehistoric times right up to the end of the 20th century. Films and interactive displays show how people here lived, fought and survived over the last 11,000 years.
References: Tallinn Tourism
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.