Aquis Querquennis is the ruins of a Roman military camp sit along a flooded section of a river. The construction of the barracks dates back to the reign of Vespasian, around the year 75, when it was likely used as a base from which to defend newly built roads connecting other, larger roads in this remote province.
The walls, arches and moat that form the foundations of this former Roman military camp can sometimes be found half submerged in the reservoir, depending on the amount of rain upriver and the status of the dam.
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.