Cocev Kamen is a hilltop cave site of volcanic origin near the town of Kratovo. Objects (bone fossils) discovered near the cave suggest human presence since the Paleolithic. Authors agree that the site served as a gathering point for sacrificial rituals from the Neolithic, during the Bronze Age, throughout antiquity until the Middle Ages as clarified by an abundance of pottery shards, stone (flint) tools and bone fragments unearthed from the surrounding areas. Several caves and rock shelters are decorated with red figurative art work. Comparison with similar sites in Bulgaria and Italy suggests that the paintings are indeed prehistoric.
Debated remains the notion that Cocev Kamen has also been used as an (astronomical) observatory.
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.