In ancient time.the emperor was said to be a son of Heaven.and therefore Heaven's supreme power was bestowed upon him.
the emperors' residence on earth was built as a repltca of the Purple Palace where God was thought to live in Heaven.
Name Such a divine place was certainly forbidden to ordinary people and that is why the forbidden City is so named.Originally called Zijin Cheng ('Purple forbidden City')
in china now it is usually called Gugong the 'Former/old Palace