Across ancient Europe, the yuletide holidays were a free-for-all, made dicey by role reversals: The poor invaded the homes of the rich, men dressed as women, and the lord bowed to the peasant. The 12 days of Christmas, from Dec. 25 to Jan. 7, were set in the mold of the Roman holiday Saturnalia: The holidays were a period of truce, when old grudges should be forgotten (at least temporarily), and anger swallowed. But despite all this brotherly love, the Christmas season had a sinister playfulness, similar to the original concept of trick-or-treating. Echoing Saturnalia’s public ridicule of society’s laws and customs, rowdy bands of peasants invaded the manor, demanding food and drink. In exchange, the lord received his subjects’ blessings and goodwill for the coming year.