Classical Term architecture began with the ancient Greeks, and was developed and elaborated by the Romans. In its purest and most familiar form, it is expressed by the temple, an oblong enclosure fronted or surrounded by columns. 

The formalized system of columns supporting an entablature Term that was developed for these temples proved extraordinarily adaptable. For centuries, it was regarded as the key to beauty in building, and the best guide to true proportion. Just as the Greeks and Romans were thought to have reached perfection in sculpture and art, so did their architecture haunt the imagination of the Western world. It was revived in the 16th and 17th centuries, and its use continued through the 19th century, alongside other revived styles such as the Gothic Term. Even in the 20th century, when Modernist architecture spread all over the world, the stream of new classical Term buildings never dried up entirely.

Britain has very little remaining from Roman times that shows the classical styles in use, so architects and builders had at first to learn about them from abroad, either by travel and observation, or indirectly from books and illustrations. The knowledge thus acquired changed slowly but constantly through the centuries, as each generation both learned more about the buildings of antiquity, and found new ways to use that knowledge to suit the needs and materials of its own time.

What makes a building classical? It is hard to give a single definition, but most will feature at least one of the following:

·         The use of one or more of the classical orders, which follow recognized forms and proportions both for the columns and for the entablature, that is the horizontal projections and mouldings above them.

·         The presence of certain other conventional features, such as pediments and balustrades.

·         A preference for symmetrical plans and façades over irregular ones. Not every classical building will fit these three rules, especially complex buildings, which use the classical styles in a great many different ways. The results can be very distant from the familiar classical temple.

Other classical buildings, known as astylar buildings, do without orders altogether.

Others use what might be called mixed styles, in which classical motifs appear in decorative combinations alongside devices from older traditions. There are also non-European styles which use columns in their own different ways.