During the Song dynasty , the city of Bianjing had three enclosures : the outer city wall , the inner city wall , and the palace at the center . The inner city was rectangular , with three doors on each side . The palace enclosure was also rectangular , with a watch tower on each of the four corners . It had four main gates : Xihua Gate to the west , Donghua Gate to the east , Gongchen Gate to the north , and Xuande Gate , also known as Duan Gate or Xuandelou , at the south . Xuande Gate had five @-@ paneled doors , painted red and decorated with gold tacks ; its walls was lavishly decorated with dragon , phoenix and floating @-@ cloud patterns to match the carved beams , painted rafters and glazed @-@ tile roof . There was also two glazed dragons , each biting an end of the rooftop ridge , its tail pointing to the sky . The symbolic function of these chi wei was explained in Yingzao Fashi :