In classical architecture, a colonnade denotes a long sequence of columns joined by their entablature, often free-standing, as in the famous elliptically curving colonnades that Bernini added to the facade of Saint Peter's Basilica in Rome, which embrace and define the Piazza. Compare the sequence of baluster forms that go to make a balustrade.
A colonnade of single columns is often termed a screen. 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. Paired or multiple pairs of columns are normally employed in a colonnade, but the porch of columns that surrounds a peripteral Classical temple (such as the Lincoln Memorial) can be termed a colonnade. Since the largest number of columns across the front of a classical temple front is normally eight (constituting an octastyle temple), it might be argued that a colonnade must have more than eight pairs. Certainly the proportions of a colonnade require that it be more than twice as long as it is tall.
At the British Museum porticos are continued along the front as a colonnade.