What was the overall situation of peripheral alert and communication in the tactics of building a city and guarding the city during the Warring States period?

In addition to the personnel on duty at each watchtower, there is an observation booth (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 boards, which are coated with soil to make it consistent with the color of the city wall and prevent enemy rockets. There is a day and night observation post inside. At a distance of 5 kilometers from the city, a warning line will be set up 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 rear, a liaison post is set up every 1.5 km to keep in touch with the cordon observation post and the city observation post with visual signals to transmit information. At that time, the visual sign was: when the enemy was found, a new flag was set up. Raise two flags when the enemy approaches the cordon. When the enemy entered the cordon, three flags were raised. They raised four flags when the enemy entered the city. Raise five flags when the enemy approaches the suburbs. At night, fire is a signal.

In addition, three scouts (1 group) have been set up in the main traffic arteries and checkpoints outside the city. Their tasks are to detect enemy actions and capture enemy spies, and patrol 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 begins to attack the city, Tingwei, the commander of the city's face-to-face garrison, will signal the report and inform the headquarters and friends about the enemy's situation. For example, at that time, it was stipulated that when the enemy approached the moat, they would beat drums in three links and set a new example. When the enemy fills the moat, they will beat drums and raise two flags. When the enemy entered the San Francisco barrier, they drummed five times and passed it and raised three flags. When the enemy entered Fengyuan, they beat 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 all sides and raised six flags.

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