The Ponts Couverts are a set of three bridges and four towers that make up a defensive work erected in the 13th century on the River Ill in the city of Strasbourg in France. The three bridges cross the four river channels of the River Ill that flow through Strasbourg's historic Petite France quarter. The Ponts Couverts have been classified as a Monument historique since 1928.
Construction of the Ponts Couverts commenced in 1230, and they were opened in 1250. As a defensive mechanism, they were superseded by the Barrage Vauban, just upstream, in 1690, but remained in use as bridges. As built, each of the bridges was covered by a wooden roof that served to protect the defenders who would have been stationed on them in time of war. These roofs were removed in 1784, but name Ponts Couverts (covered bridges) has remained in common use ever since.
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.