134 COMPARATIVE ARCHITECTURE. The dome, although described by Middleton to be of concrete, was found by Chedanne to be built of brickwork laid in almost horizontal courses up to the fourth range of coffers, and also near the central opening at the summit. The intermediate portion was not examined, but it is held that a series of arches may have been formed in this portion, so as to relieve from pressure the recessed opehings below. The lighting is effected solely by one circular unglazed opening, 27 feet in diameter, formed in the crown of the dome, and still retaining its circular bronze cornice (No. 54 c, d). This method of lighting produces an effect which is solemn and impressive ; and there may have been a symbolic meaning in thus imitating the appearance of the vault of the heavens in the temple of all the gods, the idea being that the worship of Jupiter should take place in a building open to the sky. " One great eye opening upon heaven is by far the noblest conception for lighting a building to be found in Europe." The circular portion was originally faced with marble up to the lower stringcornice, the upper portion being faced with stucco decorated with pilasters, as shown in the drawings made by Palladio in the i6th century. At the present time the walls are faced in brick with " opus reticulatum," divided by the two cornices. The dome, which has its lower portion formed in steps, was originally covered with bronze gilded plates, but these were removed to Constantinople by Constans II. in 655, and replaced with sheets of lead. The octastyle portico has monolith Corinthian columns, 46 feet 6 inches high, 5 feet in diameter at the base, and 4 feet 3 inches at the top. These support an entablature 1 1 feet high, and a pediment having an inclination of about 23 degrees. Each of the three divisions of the portico ceiling appears to have been segmental and formed of bronze plates, since removed. The old Roman bronze door frame, doors and fanlight, originally plated in gold, still remain (No. 37 a). The Temple of Vesta, Tivoli (b.c. 27-A.D. 14) (Nos. 18 c, 57 H, J, k), is another circular peripteral example, having a cella 24 feet in diameter, surrounded by a peristyle of eighteen Corin- thian columns, 23 feet 6 inches high, resting on a podium. The cella, 23 feet 11 inches in diameter internally, had two windows, and a doorway approached by a flight of steps. The columns are nearly 9f diameters high, and the capitals, of which the foliage is derived from the acanthus mollis, are one diameter in height. The reason for the difference in design between the Temple of Mater Matuta, Rome, and this example are instructive. The Roman building, placed in a low flat situation, has columns of slender proportions in order to give it the required height ; whereas the Tivoli example, placed on the edge of a rocky prominence, and
