In classical architecture, a colonnade is a long sequence of columns joined by their entablature, often free-standing, or part of a building. Paired or multiple pairs of columns are normally employed in a colonnade which can be straight or curved. The space enclosed may be covered or open. In St. Peter's Square in Rome, Bernini's great colonnade encloses a vast open elliptical space.

When in front of a building, screening the door (Latin porta), it is called a portico. When enclosing an open court, a peristyle. A portico may be more than one rank of columns deep, as at the Pantheon in Rome or the stoae of Ancient Greece.

When the intercolumniation is alternately wide and narrow, a colonnade may be termed "araeosystyle" (Gr. αραιος, "widely spaced", and συστυλος, "with columns set close together"), as in the case of the western porch of St Paul's Cathedral and the east front of the Louvre.