Introduction Beijing is one of the largest cities in China, second only to Shanghai as the nation's biggest. It is also a major transportation hub, with dozens of railways, roads and expressways connecting the capital city in all directions. The metropolitan area of Beijing had been settled in the 1st millennium BC and the capital of Kingdom Yan (?) was established there, who named it Ji (?). Ji has often been claimed to be the beginning of Beijing; but in reality Ji had been abandoned no later than the 6th century. The exact location of Ji remains unknown despite much effort in recent decades to identify the site.,