monopteros

thumb|upright|Schematic plan of a monopteros A monopteros (Ancient Greek: , from: μόνος, 'only, single, alone', and , 'wing'), also called a monopteron or cyclostyle, is a circular colonnade supporting a roof but without any walls. Unlike a tholos (in its wider sense as a circular building), it does not have walls making a cella or room inside. In Greek and especially Roman antiquity, the term could also be used for a tholos. In ancient times, monopteroi (Ancient Greek: ) served among other things as a form of baldachin for a cult image. An example of this is the Monument of Lysicrates in Athens, albeit with the spaces between the columns being walled in, even in ancient times. The Temple of Roma and Augustus on the Athenian Acropolis is a monopteros from Roman times, with open spaces between the columns.

Monopteroi were popular garden features in English- and French-style gardens, often given classical names such as "muses' temple". Many wells in parks and spa centres are covered by a monopteros. Many monopteroi have staffage structures like a porticus placed in front of the monopteros. These also have only a decorative function, because they are not needed in order to provide an entrance to a temple that is open on all sides.