Great Wall
The Great Wall was ancient China's integrated defense system, consisting of a series of high and sturdy walls and passes built by exploiting natural geographical features to stop the assaults by enemy cavalry forces. Spanning its length are various fortifications, including passes, military fortresses, cas- tles, garrison stations, and beacon towers, in addition to walls that served as the defense system's backbone. The Great Wall is an engineering marvel in ancient China and in the history of human civilization.
The history of the Great Wall can be traced back to the Western Zhou Dynasty (1046-771 B.C.). By the time of the Spring and Autumn period (770-476 B.C.), various states con- structed extensive fortifications to protect their borders. When China was unified in the Qin Dynasty (221 B.C.-206 B.C.), sections of these earlier fortifications were repaired and linked to form the renowned "10,000-li Long Wall" (2 li approxi- mately equal to 0.6 miles [1 kilometer]). From then on until the Ming (1368-1644) and Qing (1616-1911) dynasties, almost every dynasty took action to restore and rebuild the Great Wall. Over the course of more than 2,000 years, its length totaled more than 21,000 kilometers with over 43,000 historic sites. Such a colossal project is unparalleled in China and the world, earning it a spot among the "Seven Wonders of the Medieval World." Today, the remaining sections of the wall are primarily located in 15 provinces, autonomous regions, and municipalities in northern China; notable sections include the Shanhaiguan Pass in Hebei Province, the Jiayuguan Pass in Gansu Province, and the Badaling and Simatai sections in Beijing.
The Great Wall also has geographical, historical, and cultural significance. It stretches along the 400mm isoline of mean annual precipitation in northern China, serving as a dividing line between agricultural and nomadic civilizations and help- ing maintain peace between the agrarian and nomadic groups and facilitate long-term, large-scale, and continuous exchanges between them. The construction and defense of the Great Wall also promoted the extensive integration of the Han and ethnic minorities in ancient China, making significant contributions to the formation and development of a pluralistic and integrated Chinese nation. A large number of ancient literary masterpieces were based on the theme of the Great Wall, with the frontier poems of the Tang Dynasty (618-907) being the most prominent. These works add cultural meaning to the Great Wall. Over the centuries, the Great Wall has become a symbol of the Chinese nation's wisdom and strength, a testament to the Chinese people's political tradition of great unity. In modern times, it has also come to symbolize the Chinese nation's deter- mination to resist aggression and protect unity. In 1987, it was included on the UNESCO World Cultural Heritage List.
长城
长城是中国古代的军事防御工程，是依托地形地势建造的高大、坚固且连绵不断的长垣与关隘，用以限隔敌方骑兵的行动。长城不单单是一道城墙，而是以城墙为主体，以隘口、军堡、关城、卫所、烽火台等多种防御工事连接形成的一套完整的防御体系，是中国古代一项伟大的建筑工程，也是人类文明史上的一大奇迹。
长城的修筑可追溯至西周时期。春秋战国时期，列国因战争防守需要而大量修筑长城。秦代统一中国后，将列国长城进行大规模修缮、连接，筑起了"万里长城"。此后直至明清时期，历朝历代几乎都有修筑长城的行动。长城的修筑延续2000多年，历代长城总计长度超过2.1万千米，各类遗存超过4.3万处。这样浩大的工程在中国和世界上都是绝无仅有的，人们因此将长城列为世界中古七大奇迹之一。目前，长城遗存主要分布在北方15个省区市，其代表性地段有山海关（河北）、嘉峪关（甘肃）、八达岭长城（北京）、司马台长城（北京）等。
长城具有丰富的地理、历史和文化内涵，其走向与中国北方的400毫米等降水量线基本吻合，是农耕文明和游牧文明的分界线，有效维护了二者之间的和平，为两种文明长时段、大规模、持续交流创造了稳定环境。长城的修建和戍守促进了中国古代汉族与少数民族的广泛融合，对中华民族多元一体格局的形成和发展作出重要贡献。以唐代的边塞诗为代表，古代的文人墨客以长城为题材创作了大量优秀的文艺作品，丰富了长城的文化内涵。长城凝结着中华民族几千年的智慧与力量，象征着中华民族大一统的政治传统和民族意志，近代以来更成为中华民族抗击侵略、维护统一的精神标识。1987年，长城列入联合国教科文组织世界文化遗产名录。