What was the general situation of peripheral alert and communication in the tactics of building cities and guarding cities during the Warring States period?

In addition to the watchmen on duty, each watchtower has a watchtower (waiting building) every 60 meters. The outer edge of the pavilion is about 1 m above the female wall, with a square roof and three wooden boards, which are painted to match the color of the city wall and can prevent enemy rockets. There is a day and night observation post inside. In a place 5 kilometers away from the city, a cordon will be built around the city, and a three-person observation post will be set up at the commanding heights at regular intervals. From the post to the back, a liaison post is set up every 1.5 km to keep in touch with the cordon observation post and the observation post in the city with visual signals to transmit information. At that time, the visual sign was: find the enemy and set up a new flag. Raise two flags when the enemy approaches the cordon. When the enemy entered the cordon, three flags were raised. When the enemy entered the city, they raised four flags. Raise five flags when the enemy approaches the suburbs. At night, fire is a signal.

In addition, three scouts (1 group) are set up at the main traffic arteries and checkpoints outside the city, with the task of detecting enemy actions and catching enemy agents, and patrolling inside and outside the cordon at night. Once the enemy enters the suburbs, they will attack the city, and all the alert and reconnaissance personnel outside the city will be evacuated.

When the enemy began to attack the city, the garrison commander's court across the city signaled to report and informed the headquarters and friendly forces of the enemy's situation. For example, at that time, it was stipulated that when the enemy approached the moat, the drums would be used as three links to set a new example. When the enemy fills the moat, he beats gongs and drums and raises two flags. When the enemy entered the San Francisco barrier, they drummed five times and raised three flags. When the enemy entered Fengyuan, they knocked on six drums and raised four flags. When the enemy approached the city wall through Abatis, they beat drums seven times and raised five flags. When the enemy began to enter the city, they beat gongs and drums and erected six flags.

In the battle, when the defenders in the city need rear support, they also use the prescribed banner to report and notify. For example, when the death squads need support, the goshawk flag will be raised, the double rabbit flag will be raised when a large number of people need support, the dog flag will be raised when long-range weapons such as crossbows need to be replenished, the feather flag will be raised when fighting weapons such as swords and shields need to be replenished, the red flag will be raised when fire fighting equipment is needed, and the white flag will be raised when rolling stones need it.