Beacon fires were lit on the watchtowers to warn of the enemy's approach.
Tips
culture
Legend credits 燧人氏 ('the Fire-Driller') with teaching people to make fire by drilling wood. 烽燧 means beacon signals: 烽 was the night fire, 燧 the daytime smoke.
Fire radical on the left, 火, a pictograph of rising flames. It fixes the meaning on fire - both making it and signaling with it. Same family as 灯 lamp, 烟 smoke, 烧 to burn.
