At the ends of the building the two upper divisions of the cornice--namely, the projecting corona and the crowning ovolo--are made to follow the sloping line of the gable, a second corona being also carried across horizontally in a manner which can be best understood by inspecting a diagram of the corner of a Greek Doric building (Fig. 57); and the triangular space thus formed was termed a pediment, and was the position in which the finest of the sculpture with which the building was enriched was placed. In the Parthenon a continuous band of sculpture ran round the exterior of the cell, near the top of the wall. One other feature was employed in Greek temple-architecture. The _anta_ was a square pillar or pier of masonry attached to the wall, and corresponded very closely to our pilaster; but its capital always differed from that of the columns in the neighbourhood of which it was employed. The antæ of the Greek Doric order, as employed in the Parthenon, have a moulded base, which it will be remembered is not the case with the column, and their capital has for its principal feature an under-cut moulding, known as the bird's beak, quite dissimilar from the ovolo of the capital of the column (Fig. 65). Sometimes the portico of a temple consisted of the side walls prolonged, and ending in two antæ, with two or more columns standing between them. Such a portico is said to be in antis. [Illustration: FIG. 65.--ELEVATION AND SECTION OF THE CAPITAL OF A GREEK ANTA, WITH COLOURED DECORATION.] The Parthenon presents examples of the most extraordinary refinements in order to correct optical illusions. The delicacy and subtlety of these are extreme, but there can be no manner of doubt that they existed. The best known correction is the diminution in diameter or taper, and the _entasis_ or convex curve of the tapered outline of the shaft of the column. Without the taper, which is perceptible enough in the order of this building, and much more marked in the order of earlier buildings, the columns would look top-heavy; but the entasis is an additional optical correction to prevent their outline from appearing hollowed, which it would have done had there been no curve. The columns of the Parthenon have shafts that are over 34 ft. high, and diminish from a diameter of 6·15 ft. at the bottom to 4·81 ft. at the top. The outline between these points is convex, but so slightly so that the curve departs at the point of greatest curvature not more than ¾ in. from the straight line joining the top and bottom. This is, however, just sufficient to correct the tendency to look hollow in the middle.