US President Richard M. Nixon and Retinue at the Great Wall of China During a Trip to China, 24 February 1972.
Photo: Oliver F. Atkins, White House Photographer.
Nixon Presidential Materials.
National Archives and Records Administration.
City walls are some of the oldest known types of fortifications. It is known for certain that elaborate defensive walls were supposed to protect Jericho, one of the oldest known settlements in the world. Notwithstanding, walls became larger and more complex and their designs evolved to maximize the defenses that they provided. The largest fortification ever built was the Great Wall of China and it dates from about the 7th through the 4th centuries BC. The Great Wall is still regarded to be the largest engineering and building project ever undertaken by mankind.
Wall-type fortifications continued to advance beyond this time and probably reached their technical apex during the classical period. Greek fortifications during this period were designed so that overlapping fields of fire were possible from ballistae mounted in ramparts and towers. Roman fortifications continually became more sophisticated and towards the end of the period were built on sites that were naturally defensible.
Walls became ineffective for military applications due to improvements in artillery with the catapult and trebuchet being the primary devices causing their demise; later, cannon became major factors in their ineffectiveness. Nevertheless, walls continue to be extremely effective in certain defensive applications today.
Ruins of Galligo Mills, Richmond, Va., 1865.
Photo: Mathew Brady Photographs.
War Department. Office of the Chief Signal Officer.
National Archives and Records Administration.
Still Picture Branch. College Park, Maryland.