Beacon Tower

Hwaseong Fortress
1794-1796
Suwon, Korea

This beacon tower, the only one in Suwon, is located along the east wall of the fortress. Smoke signals from the five chimneys on the roof had the following meanings, according to Wikipedia: when one was lit it signalled peace, two meant the enemy had been spotted, three warned that the enemy was approaching, four meant the enemy had made it into the city, and five was an alert that fighting had begun.