The Spanish city of Almería suffered up to 52 bombings from air and sea, with a total of 754 bombs dropped during the Spanish Civil War. This led to the decision to create a system of underground shelters for the protection of approximately 40,000 civilians. These shelters measure more than 4.5 km long, and they are equipped with a surgery room and a food storage room. They were designed by the local architect Guillermo Langle Rubio, being today the most important and better preserved shelters in all Europe. These refuges have stood the most important attack in all Almería's history, the Bombardment of Almería, by the nazis in 1937.
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.