An ancient Chinese 'optical telegraph': during the day, smoke (
烽 fēng) was raised by burning wolf dung (
狼烟 lángyān); at night, fire (
火 huǒ) was lit. Beacons along the Great Wall could relay alarm from frontier to capital within hours. The famous cautionary tale
烽火戏诸侯 — King You of Zhou (
周幽王) lighting the beacons for laughs to amuse Bao Si (
褒姒) — is the Chinese equivalent of 'the boy who cried wolf'.
