Doric columns are distinguished from those of the other two orders (Ionic and Corinthian) by the absence of the supporting base, and by the shaft which has a bulge (entasis) at one third of its height.
The function of the entasis is to correct the shrinking optical illusion created by a row of perfectly truncated-cone columns.
The capital, however, is the unique element that best distinguishes the style: it consists of a swollen truncated-cone-shaped moulding, surmounted by a rectangular abacus.
