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Last edited 30 Aug 2019
Typically viewed from below, a column with straight parallel sides that taper toward the top can appear to be concave in outline. Classical designers therefore created a slight convexity (swelling) in the middle length of the column to correct the appearance of concavity. It is thought that the application of entasis also created a greater illusion of strength and height.
The word entasis derives from the Greek word ‘εντενω’ (enteino – to stretch or make taut) and the term is believed to have been first used by the Roman military architect Vitruvius (c.80-15BC).
Entasis maybe seen in classical architecture all over the world, such as on the Doric columns of the Parthenon, where it is said there is not a single straight vertical line in the surrounding colonnade (peristyle). With each vertical bowed, the projected lines are thought to meet at a point in space 3.5km away. The Renaissance architect Andrea Palladio also employed entasis and this can be seen on many of his works, such as the Villa Capra (La Rotunda), just outside Vicenza, northern Italy, built 1567-1570.
There has been much conjecture over the use of entasis in architecture because there is no evidence to fully explain why the early classical builders used the technique. Some have argued that entasis makes a column appear to bulge and therefore is expressing the notion of strength as it takes the weight of whatever is above it. This may explain the exaggerated entasis applied to the columns of the First Hera temple at Paestum, Italy, that appear to bulge significantly at their lower extremities.
Others say that there is a sound engineering explanation for applying the technique, as a column that bulges in its middle section is stronger than a column whose diameter changes in a progressive, linear way.
 Other applications
Entasis has been used in construction before and after the period of classical antiquity: it is thought that the builders of the pyramids may have been the first to use it and it has been employed on constructions elsewhere ever since.
The Inca employed entasis in their walls and doorways and it can also be seen in the monasteries and fortress architecture of Tibet and Bhutan. Building a battered (sloping) wall simply straight can make it appear to bulge outwards. Another example is the spire of the 14th century steeple of All Hallows parish church in Gedling, Northamptonshire.
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