4Derbent Fortress – Russia (circa 500 AD)
Located in the Russian republic of Dagestan, Derbent Fortress is a key structure in one of the world’s oldest continuously inhabited cities. The fortress was built by the Sassanid Persians to guard the narrow passage between the Caspian Sea and the Caucasus Mountains. With its imposing walls stretching down to the sea, Derbent served as a military choke point for centuries and played a pivotal role in regional geopolitics.
