In 567 the Council of Tours proclaimed the twelve days between Christmas and Epihany to be a sacred and festive season. Since then it has been widely accepted as a time of holiday and merriment; in many times and places all non-essential work was forbidden. In German-speaking territories the time is Die Zwölf Raunächte, the Twelve Rough Nights, a time to take precautions against the evil spirits (especially the sky-borne Wild Hunt) with noise, masks and smoke.
The Twelve Days are not calculated in the same way everywhere. In some places Christmas is counted making Epiphany the thirteenth day. In England it is particularly confusing because January 6 is Twelfth Day but January 5 is Twelfth Night.