How did Linzi City build a strict defense system?

Linzi city consists of a big city with an approximate rectangle and a small town in the southwest corner. This big city is about five kilometers long from north to south and four kilometers wide from east to west. It is where officials, civilians and businessmen live. The town is also two kilometers long from north to south and about one kilometer wide from east to west. The monarch lives in Miyagi. The city walls are all made of rammed earth, and the wall base is about 30 meters wide. A big city has an east gate, a west gate and two north and south gates, while a small city has an east gate, a west gate and two south gates. Three moats in the south, west and north are connected with Zishui. The main traffic roads in the city extend in all directions, and ten avenues are connected with the city gate. From the initial site selection to the later construction, the former and the latter complement each other, greatly enhancing the city's defense function and forming a strict defense system throughout the capital.