Nuraghe Appiu archaeological park is surrounded by a suggestive and uncontaminated environment. It was probably born as anuraghe with only one tower, to which, later, other towers have been united, connected among them by corridors, outlining a quadrilobate figure.
In its simple form the nuraghe is a flat-topped conical tower built with stones of varying size laid without grout (dry walls). The masonry consists of courses of stone laid in more or less orderly fashion. In many cases the stones were laid as they were, but more often they were dressed to facilitate their laying. In the upper part of the towers, the part most exposed, the stones are usually dressed with care to ensure a perfect fit between the different elements and thus improve stability.
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.