The dome is a semicircle, but has an open eye at its apex of nearly 30 feet in diameter ([Fig. 401]).
Fig. 401.
Half elevation of Exterior. Half section of Interior.
Pantheon, Rome. (From Fergusson.)
The dome, as viewed externally, is buried by the wall which rises above its springing to fully a third of its height, and above this rises a sort of attic crowned by six gradenæ, burying nearly an equal height, so that the dome as an external feature is far from conspicuous, appearing as a mere flattened disc.
Internally, however, it forms a covering of the noblest character. Its internal surface is deeply coffered by panels of four orders, in depth dividing the circumference into twenty-eight parts, and its height, up to about two-thirds of the distance from the springing to the crown, into five parts, the upper portion being plain. These vast panels or coffers, the larger range of which exceed twelve feet in diameter, are curiously arranged as to their sectional recessing, so as to appear perfectly symmetrical to the eye of a spectator standing beneath the centre of the dome.
The wall, up to the springing of the dome, is beautifully decorated with rich architecture in marbles of varied colour, and it cannot be doubted that the cupola—the very soul of the design—was embellished in a manner fully proportioned to the beauty of its sustaining wall; indeed, it is thought to have been coated with gilded bronze.[62] When thus perfect, it must have formed an interior of surpassing beauty, lighted as it was solely through the central eye, and the light tempered by the linen veil stretched across its rich bronze cornice, which still remains round the opening, and retains vestiges of gilding. The Pantheon can scarcely be called a daring effort of construction, because its vast solidity seems to defy all doubts as to its duration. It would be, however, absurd to suppose it to have been an early effort; for it is, as I have already said, so artificial in its construction, as clearly to prove it to be the result of long-continued practice.
The walls, which I have described as being 20 feet thick, are so only in theory, for practically they are hollowed into innumerable cells, some of them forming beautiful architectural recesses, and others merely constructional hollows.