Alconchel Castle is built in the site of Roman, Visigoth and Moorish fortifications. Today oldest parts date from the 12th century, when Alconchel was reoccupied by kings of Portuguese and León. The castle was altered in the late 14th century and 16th century for better protection against gunpowder weapons. Numerous battles between the kingdoms of Spain and Portugal took place here.
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.