entasis [Gr.,=stretching], the slight convex curvature of a classical column that diminishes in diameter as it rises. This device, as used by Greek builders, was of extreme subtlety, the freehand curvature being merely sufficient to guard the contours of the column from any appearance of inward sagging. In the Doric columns of the Parthenon, 34 ft (10.3 m) high and 6 ft 3 in. (1.9 m) in diameter at the bottom, the total convexity amounts to only 3/4 in. (1.91 cm). In Greek Doric columns the entasis began at the foot, but in the Roman orders it was confined to the upper two thirds of the column.

Convex curve given to a column, spire, or similar upright member to avoid the optical illusion of hollowness or weakness that would arise from normal tapering. Exaggerated in Greek work of the Doric order, it grew more and more subtle in the 5th–4th century BC. Entasis is also occasionally found in Gothic spires and in smaller Romanesque columns.

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