in antiquity, denotes a fatal day whereon the Romans received some memorable defeat. The word literally imports a black day; a denomination taken from the colour; which is the emblem of death and mourning. Whence the Thracians had a custom of marking all their happy days with white stones or calculi, and their unhappy days with black ones; which they cast, at the close of each day, into an urn. At the person's death the stones were taken out; and from a comparison of the numbers of each complexion, a judgment was made of the felicity or infelicity of his course of life. The dies atræ or atri were afterwards denominated nefasti and poferi. Such in particular was the day when the tribunes were defeated by the Gauls at the river Allia, and lost the city; also that whereon the battle of Cannæ was fought; and several others marked in the Roman calendar, as atræ or unfortunate.