Augustae was built as a fortified military camp in the mid-1st century, as the first fortification was made of wood and earth. The castle was naturally protected to the south by the Ogosta River, to the east and north by marshland. Access was possible only from the western side, where a fortified wall reinforced with a ditch was erected. In the 2nd-4th century Augustae developed as a Roman and an early Byzantine urban centre. Its total area reaches about 9 hа.
The fortress had the shape of an irregular pentagon extending from north to south. The fortress wall was dug inside up to 2.30 m and its thickness reached 2.50 m. Its walls were made of roughly worked stones, bonded with white mortar. The fortress had three gates - one to the west, north and east. The defence system consisted of protruding towers. The necropolis was located west of the fortress. Archaeologists have uncovered the fortification system of the Early Roman camp and the settlement dating to the Late Antiquity. The western wall with three rectangular towers and the western gate of the stone fortification have been explored. The site of the severely destroyed northern gate has also been established. Buildings have been uncovered in the inner part of the site, located in the approximate centre of the early Roman camp. In the 3rd–4th century the city was restored periodically after the invasions of the Goths. The last destructive invasion by the Avars in the 6th century marked the end of its existence.
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.