《左传·哀公·哀公七年》
百姓由城邑来保护，城邑由德行来保护。丢掉了信和仁两种德行，就危险了，还能保护什么？ 
民保于城，城保于德，失二德者，危将焉保？ 
It is the city walls that protect the people, and virtue that protects the city walls. When faith and benevolence are gone, what is there left to protect?