The term originally referred to shield and fortress, but was later used to mean dukes and princes, and then defenders of a regime, theory or proposition. Gan (干shield), a defensive weapon in old days, is used to mean to defend, while cheng (城) means inner and outer city walls or a fortress, a structure for defensive purposes. Dukes and princes were likened to gancheng (干城), in contrast with chongcheng (崇城), which means supreme city, referring to the Son of Heaven and indicating his supreme position. It is meant that dukes and princes, likened to shield and fortress, had the responsibilities to defend the Son of Heaven. Hence, dukes and princes must obey orders from the Son of Heaven. As it has evolved over time, the term generally referred to loyal and efficient defenders. Interestingly, it came to mean that not only people of lower ranks defend their superiors, but also people of high positions defend their subordinates.