Treatise on Armament Technology, Volume 231

When the Yellow Flag is employed, a Gong original: 鑼 (luo); a bronze percussion instrument used for clear, piercing signals. shall be used in coordination with it. In such cases, the eight characters: "By day observe the Yellow Flag; by night listen for the Gong" must be written in large script upon the third designated beam of the parapet wall. When the Blue Flag is employed, a Trumpet original: 喇叭 (laba); a traditional long brass horn. shall be used; the eight characters: "By day observe the Blue Flag; by night listen for the Trumpet" must be written in large script upon the fourth designated beam of the parapet wall. When the White Flag is employed, a Wooden Clapper original: 木梆 (mubang); a hollow wooden block struck with a mallet to produce a sharp, rhythmic sound. shall be used; the eight characters: "By day observe the White Flag; by night listen for the Wooden Clapper" must be written in large script upon the parapet wall. This protocol applies to all other watchtower beams and openings.

Suppose that during the day, the enemy attacks the walls beneath the "Heaven-series Number One" signaling beam. In that case, the commanding watchtower for that sector shall wave a Red Flag. If the enemy attacks the walls beneath the same "Heaven-series Number One" sector at night, the commanding watchtower shall sound the Drum Signal.

Upon these signals, the defending soldiers and laborers shall immediately enter a state of high alert original: 戒嚴 (jieyan); martial law or a state of heightened readiness.. They must wait for the striking of the signals on the left and right city towers, at which point the mobile units original: 遊兵 (youbing); literal "wandering soldiers," referring to flexible reserve units or patrols not tied to a single station. shall arrive to provide reinforcements. The watchtowers on either side shall face the enemy to deliver a coordinated counter-attack original: 摧擊 (cuiji); to smash or destroy the enemy force..

Officers and soldiers stationed at other watchtowers or beams that are not within the Assigned Ground original: 信地 (xindi); the specific sector of the wall an officer is responsible for. of the alarm are strictly forbidden from moving out of position in a disorderly fashion. Even if the various city gates are not currently under alarm, they must also...