 Yongle demoted Nanjing to a secondary capital and in 1403 announced the new capital of China was to be at his power base in Beijing . Construction of a new city there lasted from 1407 to 1420 , employing hundreds of thousands of workers daily . At the center was the political node of the Imperial City , and at the center of this was the Forbidden City , the palatial residence of the emperor and his family . By 1553 , the Outer City was added to the south , which brought the overall size of Beijing to 4 by 4 ½ miles . 
