The word "curfew" comes straight from medieval fire safety. Old French couvre-feu — from couvrir ("to cover") and feu ("fire") — named the ringing of a bell at a fixed evening hour, the signal for households to cover their hearth-fires for the night.
A Real Risk in a Wooden World
Medieval European towns were built almost entirely of timber and thatch, and a single unattended cooking fire could level a city quarter in an hour. To reduce the risk, town authorities required households to bank or extinguish their hearth-fires after dark. A bell rung from the church or town hall — the couvre-feu bell — gave the official time. After it rang, a fire was a punishable offence.
From Fire Rule to Movement Rule
By the late Middle Ages, the practical fire-safety meaning had broadened. The same evening bell increasingly signalled that ordinary people should be off the streets and in their homes for the night. By the 16th century, "curfew" in English referred not so much to the fire itself as to the hour at which everyone was expected to be indoors. The shift from "cover your fire" to "stay in your house" was completed without anyone particularly noticing.
Modern Curfews
Modern curfews come in two main forms. Civil and military authorities impose curfews to manage emergencies, unrest, or wartime conditions. Parents impose curfews on teenagers. Both senses are inherited from the medieval idea: a fixed hour after which a particular activity is forbidden. The fire-management origin is now almost entirely lost, surfacing only when someone goes back to the dictionary — or when an unusually heavy bell still rings, in some old English towns, at eight in the evening.