The first Vasknarva order castle (Neuschloss) was founded in 1349 on the northeastern border of Old Livonia. 1427–1442 a new castle (Vastne-Narva) was built, which became the centre of the vogtei of the Livonian Order. The castle was wracked in the Livonian War. Until the Great Northern War it was a fort of great importance, commanding the mouth of the Narva River. It has been known in Russian chronicles either as Syrensk or Syrenets. According the folklore St. Olga of Pskov narrowly escaped drowning when crossing the Narva rapids at Syrenets. Nowadays only parts of 3 meters thin walls have survived, mainly on the northern side.
Reference: Wikipedia
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.