1911 Encyclopædia Britannica/Bailey

BAILEY (said to be a corruption of Ballium by some, and derived by others from the Fr. baille, a corruption of bataille, because there the soldiers were drilled in battle array), the open space between the inner and outer lines of a fortification. Sometimes there were more than one, as the Inner and Outer Bailey; there are in England the Old Bailey at London and at York, and the Upper and Nether Baileys at Colchester.