Daugavpils Fortress, also known as Dinaburg Fortress is the only early 19th century military fortification of its kind in Northern Europe that has been preserved without significant alterations. For a long time it was a defense base of the western frontier of the Russian Empire. Planning of the fortress began in 1772 by decree of Tsar Alexander I of Russia, shortly after the First Partition of Poland when Latvia ceded to Russia and construction began during Napoleon"s attack of the Russian Empire in 1810. In 1812, the fortress was attacked by the French Army of 24,000 men. The fortress was still under construction and was defended by 3300 men and 200 cannons.
Construction of the fortress, despite lengthy delays, serious floodings and slow construction work, was completed in 1878. Latvian independence was officially recognised by Soviet Russia in 1920 and between 1920 and 1940 the fortress became home of the Latvian army. During World War II, the hostage camp Stalag 340 was set up in the fortress.
Today fortress is the site of the Daugavpils Mark Rothko Art centre.
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.