[Illustration: FIG. 135.--THE PANTHEON, ROME. GROUND-PLAN.]

[Illustration: FIG. 136.--THE PANTHEON, ROME. EXTERIOR.]

The Pantheon is the finest example of a domed hall which we have
left. The building, which forms the church of Santa Maria ad Martyres,
has been considerably altered at various times since its erection, and
now consists of a rotunda with a rectangular portico in front of it.
The rotunda was most probably erected by Agrippa, the son-in-law of
Augustus, in B.C. 27, and is a most remarkable instance of clever
construction at so early a date. The diameter of the interior is
145 ft. 6 in., and the height to the top of the dome is 147 ft. In
addition to the entrance, the walls are broken up by seven large
niches, three of which are semicircular on plan, and the others,
alternating with them, rectangular. The walls are divided into two
stories by an entablature supported by columns and pilasters; but
although this is now cut through by the arches of the niches, it is at
least probable that originally this was not the case, and that the
entablature ran continuously round the walls, as shown in Fig. 137,
which is a restoration of the Pantheon by Adler. Above the attic story
rises the huge hemispherical dome, which is pierced at its summit by a
circular opening 27 ft. in diameter, through which a flood of light
pours down and illuminates the whole of the interior. The dome is
enriched by boldly recessed panels, and these were formerly covered
with bronze ornaments, which have been removed for the sake of the
metal. The marble enrichments of the attic have also disappeared, and
their place has been taken by common and tawdry decorations more
adapted to the stage of a theatre. But notwithstanding everything that
has been done to detract from the imposing effect of the building by
the alteration of its details, there is still, taking it as a whole, a
simple grandeur in the design, a magnificence in the material
employed, and a quiet harmony in the illumination, that impart to the
interior a character of sublimity which nothing can impair. The
rectangular portico was added at some subsequent period, and consists
of sixteen splendid Corinthian columns (Fig. 138), eight in front
supporting the pediment, and the other eight dividing the portico into
three bays, in precisely the same way as if it formed the pronaos to
the three cells of an Etruscan temple.

[Illustration: FIG. 137.--THE PANTHEON, ROME. INTERIOR.]