BAY, an architectural term for any division of a building, be tween vertical lines or planes, especially the entire space included between two adjacent supports; thus the space from pier to pier in a church, including that part of the vaulting or ceiling between them, is known as a bay.
A term also applied to a roofed structure projecting from a wall and one storey high, a bay window being such a structure. When a bay window is carried on brackets, or a corbel, it is called an oriel. Bay windows came into use during the late Gothic period. Although found throughout Europe, they are peculiarly character istic of England. They usually occur at the end of the great hall of large Tudor and Jacobean manor houses and castles, reserved for the lord's dais, from which they open. Occasionally there is one on each side of the hall at each end of the dais. Befitting their position, they are often extremely rich, with fan vaults and window seats at the sill. They are also found in similar positions in the great halls of the English colleges. During the Jacobean period their use was much increased and they are found on the fronts of houses wherever an accent was desired.