entasis n : a slight convexity in the shaft of a column; compensates for the illusion of concavity that viewers experience when the sides are perfectly straight [also: entases (pl)]

English

Etymology

Modern Latin, from Ancient Greek έντασις (entasis) "tension, straining", from εντείνω (enteino) "to stretch or strain tight".

Pronunciation

IPA: /'ɛntəsɪs/

Noun

entasis

1. a slight curvature introduced into the shaft of a column to create the impression of concavity; a deliberate bowing

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 bulge slightly in the middle.

Examples

Probably the first use of entasis was in the construction of the Egyptian pyramids, but it can also be observed in Classical period Greek column designs, for example in the Doric-order temples in Segesta, Selinus, Agrigento and Paestum. It was only very rarely used in Hellenistic and Roman period architecture. The temples built during these periods were higher than those of the Greeks, with longer and thinner columns. Noted architects such as the Renaissance master Andrea Palladio also used it in their buildings.

More recently, Rolls-Royce cars all made use of it in their radiator grills to give an illusion of greater solidity.

Purpose

The early Classical builders did not leave an explanation of their reasons for using entasis, and there are several differing opinions as to its purpose. Some descriptions of entasis

state simply that the technique was an enhancement applied to the more primitive conical columns to make them appear more substantial. Trevelyan believed that the effect represented strength by imitating the swelling of a strained muscle. This accords well with the etymology of the word, from the Greek meaning 'to strain'.

Another popular view is that entasis was intended to correct an optical illusion that makes cylindrical columns appear pinched and flat surfaces appear convex. This explanation was given by Hero of Alexandria, for example.

However, it does not explain the case of one well-known example, Paestum, where the entasis is so pronounced that it creates an obvious curvature, not an illusion of straightness. Conversely, in the Parthenon, the entasis is so subtle that it has almost no effect on the apparent shape of the columns, so is insufficient to correct any supposed illusion of curvature.

It has also been argued that a 'stunted cycloid' column that bulges in the middle is stronger than a column with straight sides.

Literature

• Thomä, Walter: Die Schwellung der Säule (Entasis) bei den Architekturtheoretikern bis in das XVIII. Jahrhundert. Dresden 1915.

References