What examples can illustrate that field fortifications are extremely widely used and important means of combat by both offensive and defensive sides?

In the fifty-fourth year of Zhou Nanwang (26 1), when Qin Jun attacked Zhao Shangdang (east and southeast of Shanxi), Shangdang defenders were forced to retreat to Changping (north of Gaoping, Shanxi) to join reinforcements led by Zhao General Lian Po. In several small battles, Zhao Jun was defeated. Lian Po then adopted the operational policy of building a base and sticking to it, avoiding decisive battle and waiting for an opportunity to attack the new with the old. In the east-west area near Jinmen Mountain in the north of Changping, near 10 km, a defensive belt consisting of several circular camps was built, and the city wall could not be hardened. He launched many attacks and captured the support points of three circular positions, such as the east base and the west base (Gaopingxi) of Zhao's warning position, but he never broke through Zhao's main position, forming a situation in which the two camps confronted each other from a distance. Qin Jun's overseas exploration was unfavorable for a long time. Prime Minister Qin sent spies to Zhao, spreading rumors that Lian Po surrendered easily and slandered Lian Po. The prince of Zhao suspected that Lian Po was afraid of war, so he replaced Lian Po with Zhao Kuo. Qin was also reassigned as the main general. After Zhao Kuo took office, he changed Lian Po's operational policy of giving priority to defense and organized attacks. In view of Zhao Kuo's reckless psychology of underestimating the enemy, Tian Lei adopted the operational policy of feinting and losing, lured the enemy from the rear of the established position and destroyed it. Zhao Kuo carried out several small-scale exploratory attacks, and Tian Lei ordered the troops to retreat. Zhao Kuo then led the main force to launch a general assault on Qin Jun, and was blocked in front of the position when he entered the fortified area of Qin Jun. Immediately command 25,000 mobile troops pre-deployed on the two wings, detour behind Zhao, and cut off their retreat back to camp; At the same time, 5000 elite cavalry were sent to the vicinity of Zhao Jun's base-building position. Using their quick mobility and strong impact on the infantry, they cut off the connection between the remaining troops of the Zhao army camp and the capital Handan, and the Zhao army was divided into two independent parts. Zhao Kuo's main force, in a dilemma, was forced to hastily build a circular position on the spot and turn to defense. Qin Jun built an inward barricade around Zhao and surrounded Zhao. Zhao Jun was trapped for 46 days. Due to lack of food, he broke through many times and was repelled by Qin Jun who relied on the base position. Zhao Kuo was advancing and was shot dead by Qin Jun's crossbow. All the 400,000 Zhao troops trapped in the two places surrendered. It can be seen that field fortifications are an important means of combat widely used by both offensive and defensive sides.