A colonnade is an architectural feature made by spacing columns at regular intervals. Commonly, a colonnade appears in the form of a line of columns, although a colonnade may also be several layers deep. Many people associate the colonnade with classical architecture, since colonnades were common features on Greek and Roman temples and other public buildings. They continue to be used on formal public buildings like museums and courthouses to lend these structures an air of gravity.
This architectural feature can be used in a number of ways. Classically, a colonnade lines a portico, a type of covered porch which leads to the entrance of a building. For an iconic image of a portico, look up a photograph of the Parthenon in Greece; the Parthenon has a very impressive portico lined with giant columns. Colonnades can also line covered walkways which may lead between buildings or through formal gardens.
A colonnade is also a a defining feature of a basilica, a structure with a large open central space bordered by a colonnade. By passing through the columns, people can move from the central open nave to smaller enclosed spaces; in classical cultures, a basilica was an important structure which often held administrative officials along with an open market. Mimicking the basilica design, a colonnade sometimes lines an open courtyard, especially in Mediterranean architecture, where a central open breezy space can keep a house cool in the hot summer months.
The size and design of a colonnade can vary widely, and the columns made be made from materials like limestone, marble, or even wood, in which case they are usually painted. In formal buildings, the columns are often massive, to complement the size of the building and presumably to intimidate visitors. More slender, small columns are used in architecture for formal homes; Regency architecture, for example, often featured modest colonnades as features in homes and public structures. This architectural style developed from the neo-Classical school of architecture, which also integrated a lot of columns.
The columns used to construct a colonnade can be of any style. In most cases, they are used as structural supports for a covering or the building that they accompany, although it is possible to use free-standing columns in a colonnade. Free standing colonnades sometimes appear in formal gardens, where the designer wants to use an architectural feature without overwhelming the viewer with a covering.