One of the most wonderful refinements of Greek architecture was the attention paid to optical deceptions, and the correction of these by the curvature of all straight and horizontal lines. It has been mentioned that the peripteral columns did not stand mathematically upright, all the axes being inclined inwards; the discovery of this fact was followed by a publication, made by the architect Hoffer in 1838, which maintained that no perfectly level line existed upon the entire temple, the horizontals being curved slightly upwards. Hoffer’s assertions were verified by the micrometrical studies made by Penrose, in 1846, upon the Parthenon, the so-called Theseion, the Propylæa, Erechtheion, and the Temple of Olympian Zeus in Athens, and afterwards upon the temples of Nemea and Segesta. His measurements make evident a curvature of 0.069 m. in 30.876 m. upon the front of the Parthenon, and of 0.108 m. in 69.525 m. upon its sides. Though so very slight a deviation is not readily apparent, there are no mathematically rectangular forms upon the entire building; the corner metopes are, for instance, trapezoidal. Whether these curves, the existence of which is not to be denied, were really intentional, was questioned by Boetticher, but it has been proved beyond a doubt by the further investigations of Ziller. The motive for the adoption of refinements, so extraordinarily delicate and difficult of execution, was the same desire to correct displeasing optical deceptions which prompted the entasis of the columns and the inclination of their axes from the vertical. The apparent deviation of the lines, sagging from the horizontal, was most disagreeably apparent upon the front entablature—the base of the gable triangle, which, when straight, invariably appears concave, while a corona, in reality curved upwards, presents itself to the eye as perfectly level. By a deviation from the absolutely horizontal, the appearance of greater correctness was attained.
The peripteral columns of the Doric style worthily express the peculiar character of the Dorians by their simple dignity. By them a passage was formed around the cella, the pteroma, the ceiling of which was most richly decorated with cofferings. (Fig. 141.) So short a span was here required of the horizontal beams that it was possible to translate them into stone simultaneously with the outer entablature; this seems to have been universal in the larger peripteral temples, that of Zeus in Olympia possibly being an exception. The ceiling did not remain in its original position, resting upon the epistyle, but, with the increased dimensions of the stone frieze, was considerably elevated. The spaces between the lintels were closed by slabs of stone which retained the form of the original wooden cofferings, being hollowed by stepped lacunæ, diminishing in size. A transitional moulding was placed in each angle formed by a vertical and horizontal surface. Upon the coffered ceilings of Attic monuments (Fig. 142) this member is the Lesbian cyma, supplemented by an astragal, these signs of an Ionic influence being further noticeable in other parts of these buildings. The wall of the cella, though surrounded by the pteroma, still bears traces of the entablature, which, as shown above, preceded the outstanding columns; the triglyphs and metopes are repeated, or in their place is a frieze of sculptured reliefs, in which the isolated carvings of the metope become continuous and connected. At times there remain beneath the latter the tænia, regulas, and trunnels—only to be explained and justified as the reminiscences of portions of an originally well-founded decoration which had, in part, been gradually supplanted.
The cella itself, within the pteroma, appears in plan either without columns, as a temple in antis, as a prostylos, or as an amphiprostylos, thus supporting the assumption that these were the original forms of its development. The cella was often greatly increased in length; this made its transverse division desirable, and there resulted the front portico, or pronaos, the principal hall of the temple, or naos, and the space partitioned off at the rear, called, analogically, the epinaos. An especial chamber of the building was at times isolated to serve as a treasury; this was known as the opisthodomos. (Fig. 143.) The pronaos, whether with or without columns, was closed, if at all, only by a light bronze grating; from it a wide portal, occupying almost the entire division wall, opened into the naos. Its upper part was fixed, but entrance was afforded through its lower part by folding wings. The grooves worn by the doors are still visible upon the Parthenon floor. The interior was disproportionately narrow, a result of the peripteral enclosure and of the limitations imposed by the gable, which would have become too high and heavy if the front had been greatly widened in favor of the interior breadth; moreover, the horizontal ceiling was unfavorable to width, which was limited to the natural span of the beams.
The possibility of admitting much light had been given up with the change in the position of the entablature and metopes. Notwithstanding the size of the door, sufficient daylight could not enter through this; it was itself in the shadow of the pteroma, and generally, also, of a pronaos. But little illumination was required for the small chapel when this served solely as a receptacle for the sacred image. A dim and mystical twilight was easily obtained by the use of one or more perpetually burning lamps, which could only have been favorable to the artistically unpretentious interior. It was otherwise with the larger and more important temples, opened for festive assemblages. Their interiors were divided by architectural members, and contained manifold works of art and objects of value—a varied richness, which called for an increased splendor of light, possible only by artificial illumination.[G]
In the desire to increase the available space of the temple interior, the enclosing walls were advanced more closely to the columns of the peripteros, thus decreasing the width of the pteroma; while the hall was divided by two rows of inner shafts into three aisles, the outer two of which, considerably narrower than the middle, were partitioned into two stories by the introduction of galleries, accessible by staircases at either side of the chief portal.