The three orders of Classical Greek architecture are the Doric, the Ionic and the Corinthian. The most marked difference between these three orders is the different types of columns that each employs.
The Doric order is the simplest of the three. In Doric architecture, all of the fluted columns share the same base, and their capitals consist of two parts: a convex shape called an abacus and a rectangular shape known as an echinus. The columns tend to be squat.
Columns in Ionic architecture are thinner, but they still taper toward the bottom. Each Ionic column has its own base. On Ionic capitals, the echinus has two volutes, or scrolls, resting on a base of palm-leaf ornamentation.
Corinthian columns are also slender, bulging slightly in the middle. Each column has its own base, and the elaborate capitals display a bell-shaped echinus decorated with acanthus leaves and scrolls.