Walls are a well-known part of structures and settlements since the advent of humanity.
City states in the Ancient times had important buildings, palaces serving as a main hub: storage for goods, political institute for exerting control and a cultural interest point. As a result, this building's significance made it the most vulnerable of all and it required the utmost defensive measures from the court. Walls were a simple means of making break-ins harder and soon became necessary to provide unfathomable advantages to the defensive garrison. Walls were initially made of earth and wood, however stone proved to be the most effective and durable material for constructing them.
Walls were often supported with other components such as towers, bastions and gates. They got additional features to cover and help the defenders as much as possible, such as arrowslits and other holes to pour hot liquids through them. As a result, they were very hard to break by conventional human tools, so it required the use of mechanic siege devices and explosives. Catapults, tunnels and later cannons were invaluable in this task. Walls had particular significance till late 19th century.