The Pont d'Aël is a Roman aqueduct, located in the comune of Aymavilles in Aosta Valley, northern Italy. It was built in the year 3 BCE for irrigation purposes and supplying water for the newly founded colony of Augusta Praetoria, which is now known as Aosta. The water was directed through a neighbouring valley 66 m above the floor of the Aosta valley, through a sophisticated system. The aqueduct is 6 km long in total. In addition to its unusual position, the construction, which was originally thought to be a three-story structure, shows more unique features such as a control corridor below the water line, as well as explicit private funding. Today, the water channel of the aqueduct serves as a public walking trail.
Besides the Pont d'Aël, two other Roman bridges in the Aosta valley are still intact: the Pont-Saint-Martin in the town of the same name and the Pont de Pierre in Aosta.
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.