The Castle of Trezzo sull'Adda is located on a hill within a bend of the Adda river and from this protected on two sides. On the remaining side it is closed by a wall and a 42-meter high tower. Part of the castle was the fortified bridge over the river, destroyed in 1416.
The site was inhabited since prehistoric time by Celtic populations and after the VII century hosted a Longobard settlement, which was also at the origin of the first fortification on the hill. In 1370 Bernabò Visconti, lord of Milan, ordered the construction of a new caste, which was built on the remains of the previous fortress and completed in 1377.
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.