Astragal: a convex moulding with a profile semi-circular, like that of the Torus, only smaller in width. Often decorated with Bead and Spool ornament.
Astylar: used of a façade, not treated with columns.
Asymmetries: deviations from geometrical symmetry and precision; such as substituting a slight curve for horizontal and vertical straight lines; varying slightly the spaces between columns, setting columns on a curving instead of a straight line, and so forth. Refinements which Hellenic, Byzantine, and Gothic architects introduced to give flexibility and rhythm to their structures. See Refinements.
Atlantes: See Caryatid.
Atrium: in Roman houses an entrance court open to the sky, but surrounded by a covered ambulatory. In Early Christian architecture, a similar entrance court in front of churches.
Attic: the upper story of a building, above the cornice.
Axis: an imaginary line, about which an architect arranges the symmetry of his design. The main axis usually runs through the longest direction of the building and may be intersected at right angles by a second axis. See Crossing.
[B]aldachino: or Baldachin: a canopy supported on uprights; used especially to surmount an altar.
Baluster: a small ornamental pillar supporting a rail or coping; the whole structure being called a Balustrade.
Balustrade: See Baluster.