Further, for fear that an enemy might try to tunnel into the city, the paving was made many layers thick - seven layers lengthwise and eight layers crosswise, totalling fifteen layers.

• 据估计有一千二百万块独立的砖用于外墙。此外，为了防止敌人打地道进入城内还铺设了很多层地砖，七纵八横，共十五层。