Arabesque, a style of very light ornamental decoration.
Archaic, primitive, so ancient as to be rude, or at least extremely simple.
Archivolt, the series of mouldings which is carried round an arch.
Arena, the space in the centre of an amphitheatre where the combats, &c., took place.
Arris, a sharp edge.
Astragal, a small round moulding.
Atrium, the main quadrangle in a Roman dwelling-house; also the enclosed court in front of an early Christian basilican church.
Baptistery, a building, or addition to a building, erected for the purposes of celebrating the rite of Christian baptism.
Basement, the lowest story of a building, applied also to the lowest part of an architectural design.
Bas-relief, a piece of sculpture in low relief.