The Great Wall of China is the longest in the world and has a main-line length of 3460km 2150miles - nearly three times the length of Britain - plus 3530km 2195miles of branches and spurs. Construction of the wall began during the reign of Qin Shi Huangdi (221-210BC). Its height varies from 4.5 to 12m 15 to 39ft and it is up to 9.8m 32ft thick. It runs from Shanhaiguan, on the Gulf of Bohai, to Yumenguan and Yangguan and was kept in repair up to the 16th century. Some 51.5km 32miles of the wall have been destroyed since 1966, and part of the wall was blown up to make way for a dam in July 1979.
Comments below may relate to previous holders of this record.