BIHOUAC, BIOUVAC, or BIVOUAC, from the German wegwatch, a double watch or guard, originally meant a night guard or a detachment of the whole army, which, during a siege, or in the presence of an enemy, marched out every night in squadrons or battalions to line the circumvallations, or to take post in the front of the camp, for the purpose of securing their quarters, preventing surprises, and obstructing supplies. When an army does not encamp, but lies under arms all night, or when, from being unprovided with tents, the soldiers either pass the night around the watch-fires in the open air, or seek such shelter as they can find or construct upon the spot, it is said to bivouac; and this is now the only sense in which the term is employed.