entasis

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.

entasis. In Classical architecture shafts of columns have a greater diameter at the bottom than at the top: the diminution does not result in slightly battered straight inclining slides, but a subtly convex curved swelling called entasis. In the Greek Doric Order from Paestum the shafts are much smaller at the tops than the bases, and the entasis is very obvious. Entasis can also be found on walls, spires, and towers. Entasis may have been noticed first by Allason in c.1814, but it was subsequently confirmed by C. R. Cockerell and Haller von Hallerstein. Allason published a paper in the Quarterly Journal of Science and Arts (1821) on the subject (but was indebted to Cockerell for material), and F. C. Penrose followed with detailed discussions in the 1850s.