Entasis (Greek ἔντασις " tension " ) refers to the swelling of the shaft of a column. It occurs mainly in temples of the archaic and classical period, both the Doric and the Ionic order. Most affected is the great Greek temples of southern Italy and Sicily. It is caused by an arc-shaped non- linear taper of the column diameter, the accelerated mainly from the lower third point, or the center of the stem to the top. Ancient drawings of Entasis - design have been preserved on Didymaion at Miletus. The swelling ' never exceeds the lower column diameter to thickness.

As the curvature of the Stylobaten and the architrave and the inclination of the columns and walls is the Entasis according to Vitruvius (III 3, 13 ) of the optical enhancement of the building, it should be the eye " pleasing ".

On buildings of the Hellenistic frequently no Entasis is detectable. Nevertheless Hermogenes considered at the beginning of the 2nd century BC the Entasis on the columns of his temples. In the Roman architecture of the imperial age, the Entasis was usually no longer running as uniform curvature, but was told the shaft in two straight tapered and rounded areas on only the impact area.

In southern France known in the early Romanesque upper church of the abbey of Saint- Martin du Canigou monolithic columns with Entasis.

During the Renaissance Entasis was reintroduced into the architecture by Andrea Palladio.