Built by the Teutonic Knights in 1350, the Great Mill with its rising tiled roof is the grandest civil construction in Gdańsk. Until 1356 when the Radunia Canal was built, the mill was powered by slaves turning 18 huge wheels. It was the largest industrial plant in Europe during the Middle Ages and functioned until the end of WWII. Unfortunately, this treasure has since been turned into a shopping centre. At least there's a small exhibition of old equipment from the mill. The surrounding grain and flour stores, dating to 1400, are home to a few small shops.
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.