The word curfew derives from the Old French phrase couvre-feu, which means “cover fire.” Under a law imposed by William the Conqueror, all lights and fires had to be covered by 8 p.m. to reduce the risk of conflagration in towns still built largely of timber.

The practice spread through medieval Europe. Writes historian Roger Ekirch, “Not only were streets swept of pedestrians, but homes still aglow after the curfew bell ran afoul of authorities. Besides incurring fines, offenders faced the risk of incarceration, especially if caught outdoors.”

(At Day’s Close: Night in Times Past, 2006.)