Entasis
 smARThistory – Ancient Greek Temples at Paestum, Italy
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In architecture, entasis is the application of a convex curve to a surface for aesthetic purposes. Its best-known use is in certain orders of Classical columns that curve slightly as their diameter is decreased from the bottom upward. It also may serve an engineering function regarding strength.
The word we apply to the design principle is used by the Roman architectural historian Vitruvius, and derives from the Greek word εντείνω (enteino), "to stretch or strain tight". Creating the illusion of greater strength or perception of height may have been an objective in the application of entasis.
Examples of this design principle may be found in cultures throughout the world, from ancient times to contemporary architecture. The first known use of entasis was in the construction of Egyptian pyramids.
It also may be observed among Classical period Greek column designs, built a thousand years later, for example, in the Doric-order temples in Segesta, Selinus, Agrigento, and Paestum.
It was used less frequently in Hellenistic and Roman period architecture. The Roman temples built during these periods were higher than those of the Greeks, with longer and thinner columns.
Chinese carpenters of the Song Dynasty followed designs in the AD 1103 Yingzao Fashi (Treatise on Architectural Methods or State Building Standards) that specified straight columnns or those with an entasis on the upper third of the shaft.
Noted architects, such as the Renaissance master Andrea Palladio, also used entasis in the designs of their buildings.
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