In library science and architecture, a stack or bookstack (often referred to as a library building's stacks) is "a narrow-aisled system of free-standing iron uprights, extending uninterruptedly from the foundations to the top floor, adapted to bearing adjustable shelves and supporting the entire weight of the floors, roof, shelving, and books"—​the shelving "row on row, tier on tier, with only enough vacant space to give access to books."In contrast to the structural relationship found in most buildings, the floors of a bookstack do not support the shelving, but rather the reverse, the floors being attached to, and supported by, the shelving framework.[citation needed] Typically, even the load of the building's roof, and of any non-shelving spaces above the stacks (such as offices), are transmitted to the building's foundation through the shelving system itself. The building's external walls provide protection but no significant structural support.The first modern stacks were built in 1877 as an addition to Harvard University's Gore Hall.