The Pronoas had
sixteen
monolithic round pillars of Egyptian granite. Originally eight were
gray-green
and eight were pink, but three have subsequently been replaced, two of
which with red granite pillars from the Alexandrine Baths near San
Luigi
dei Francesi near Piazza Navona. Four more square pillars are at the
rear,
but they are sometimes counted as part of the intermediate structure.
The
intermediate building is higher than the porch and had its own peaked
roof,
upper-floor side rooms and upper level porches. The pronoas and the
intermediate
building and other surrounding structures apparently were designed to
block
the view of the rotunda from the outside. The porticoed square in front
of the porch was also constricted to prevent viewing of the dome from
outside.
The whole complex appears to have been assembled with the idea of
inspiring
awe in the first time visitor, who would walk into a perfectly normal
looking
temple and, instead of a "noas" chamber for the image of the god, would
find himself in that vast and sumptuously embellished domed rotunda!
The
effect still works even for those who have visited the Pantheon often
and
know its shape and size.
Hadrian, known as a
philosopher
emperor because he committed his intentions and emotions to writing,
said
this:
"My intentions
had been
that this sanctuary of All Gods should reproduce the likeness of the
terrestrial
globe and of the stellar sphere...The cupola...revealed the sky through
a great hole at the center, showing alternately dark and blue. This
temple,
both open and mysteriously enclosed, was conceived as a solar quadrant.
The hours would make their round on that coffered ceiling so carefully
polished by Greek artisans; the disk of daylight would rest suspended
there
like a shield of gold; rain would form its clear pool on the pavement
below,
prayers would rise like smoke toward that void where we place the gods."
The dimensions are shockingly grand.
The rotunda is 142 feet (43.3 meters) in diameter and above it is a
perfectly
hemispheric dome of exactly the same diameter and the same center
height:
Hadrian's 142 foot "likeness of the terrestrial globe and of the
stellar
sphere" was a perfect fit. The oculus or eye, the circular opening at
the
top of the dome had a diameter of 27 feet (8.2 m). A row of windows on
the drum of the rotunda provided additional light, and there were
openings
to allow light from above into the interior niches.
The foundation below the
circular
wall of the rotunda is 26 feet (8 m) wide and 15 feet ( 4.5 m) deep and
is made of pozzolana cement (lime, volcanic pozzolana sand first found
near Pozzuoli near Naples, and water tamped down over layer of dense
stone
aggregate -- the predecessor of modern "portland" cement, the name of
which
is probably itself a corruption of "pozzolana".) The thick circular
wall
of the rotunda, also of pozzolana cement and cloaked with a layer of
brick,
rose exactly 71 feet from the foundations -- half the diameter of the
sphere
-- before breaking inward to form the coffered dome.
The wall of the rotunda
has seven
interior niches -- the entry from the pronoas occupies the eighth
position
-- and there are chambers between them with openings to the exterior.
Modern
engineers who have studied the structure say that these niches and
chambers
are the reason that the building has survived. Cracks that developed in
the drum over the millennia, cause by settling and movement of the
swampy
subsoil and by earthquakes, were directed upwards along the thinner
centerlines
of the niches and chambers, and that resulted in what are now, in
essence,
sixteen thick cement pillars supporting the dome. Without the
niche/chamber
pattern, which apparently was used only to minimize the total weight of
the building, the cracks may have radiated randomly, bringing down the
dome. (Those cracks were carefully mapped in the 20th century and are
constantly
monitored using modern highly accurate sensors. Nothing to worry about,
say the structural engineers, but if the ground shakes, do exit the
building
with all possible speed.)
Like the rest of the
structure,
the dome is of pozzolana cement. The interior shape is, as noted above,
hemi-spherical and coffered to reduce weight. The outer surface steps
inward,
gradually reducing the thickness of the dome wall. The aggregate
material
mixed with the cement in the lowest part of the dome is dense volcanic
stone, and less dense materials are incorporated as the dome rises to
the
oculus, again to reduce weight: at the top the aggregate is light
pumice,
and some small empty clay jars are also mixed in. Modern coring
indicates
that the entire dome was essentially one continuous "pour" of cement.
There
had to have been continuous mixing of batches of cement to be poured
over
the gradually lightening layers of aggregate*, and the planning and
execution
of such a great project would have to have been extremely meticulous.
There
are no known pouring discontinuities in the cement structure from the
top
of the foundations up to the oculus. The cracks in the drum radiate
upward
into the dome in no particular pattern, and this means that the dome is
less stable than the drum. The monitoring engineers say there's nothing
to worry about.
Once the cement structure
was completed
(the bricks around the drum of the rotunda were inserted concurrently)
decoration could begin. Fine multicolored marbles were reportedly used
on the interior, and statuary, probably naturalistically painted
marbles
were installed the interior niches and inside and along the top of the
pronoas and in the niches and upper porches of the intermediate
building.
Exposed external surfaces were covered with travertine. There is no
evidence
that the outside surface of the rotunda drum was covered in travertine:
adjoining buildings would have hidden most, if not all, of the exterior
so there was no reason to cover it with costly stone. (What travertine
there was on the exterior was later highjacked for the façade of
St. Peter's Church in the Vatican.) The dome was covered with gold
plated
bronze, some of which was taken by the Byzantine Emperor Constans 2 in
663 AD and the remainder of which was used by Bernini when he cast the
columns for the baldachino in St. Peter's -- a little was left to make
a nice cannon for Castel Sant'Angelo. Bronze trusses supported the
ceiling
of the pronoas. They, along with the bronze ring that lined the inside
of the oculus, eventually became the bells of St. Peter's,. The bronze
doors, although heavily restored, are thought to be original (some
sources
say they were almost completely recast during the renaissance.)
Only the merest traces of
the decoration
of the triangular faces above the porch and on the connecting building
remain: there are holes, into which pins for mounting (presumably)
bronze
figures would be inserted, and there are a few projecting rectangular
stones
of unknown purpose in each of the lower corners on the upper face.
Mounting-pin-hole
specialists (everybody specializes in something!) suppose that some
kind
of wreath or other round ornament was in the center of the lower
triangle.
The marbles, statues,
decorations,
altars and tombs now inside the Pantheon are definitely not original
equipment.
Most were added during the renaissance, but there are some 19th and
20th
century tombs. Among those entombed in the building are Raphael and his
girlfriend -- he was forced to marry someone else by his patron
Cardinal.
King Victor Emmanuel 2 is in the ornate box on the right hand side
(died
1878) and a lamp above it burns in honor of Victor Emanuel 3 (died
1947).
Directly across the wide rotunda is the tomb of King Umberto 1, who was
assassinated in Rome in 1900 and his extremely popular wife, Margherita
di Savoia.
The above
is just a tiny
scratch
on the surface of what is known about the pantheon. Two good printed
sources
are "The four books of Architecture" by Andrea Paladio, written in 1570
(available in English translation on-line and at better Roman
bookstores),
and "A New Topographical Dictionary of Ancient Rome" by Lawrence
Richardson,
Jr., available from the same online sources and bookstores. There are
also,
of course, scholarly and popular volumes and multi volume works
dedicated
to the building, some of the best, naturally, only in Italian.
P.S.: It is often said
that the
Pantheon is the only temple structure in continuous use since ancient
Roman
times. That's not true. It was abandoned as a temple in the fifth
Century
and was not reopened again until 608/9 when Emperor Phocas ceded it to
Pope
Boniface 4 so that it could be turned into a church. It is, therefore,
definitely not a Constantinian structure, as some guides/guidebooks
would
have you believe. The church again fell into disuse during the period
when
the papacy was resident in Avignon (1309-77) and was rededicated at the
end of that period.
Internet links:
Le
panthéon
Pantheon
-- Platner & Ashby
Pantheon
- Koskimies
Pantheon
-- Great Buildings Online
Pantheon
-- Maecenas
Pantheon
images -- Popolo Project (1st of several pages)
Pantheon
No.1(of 4) - History of
Pantheon-romaonlinguide
Piazza della
Rotonda
- Romartlover
Romeguide
- The Pantheon
The
Pantheon -- Rodolpho Lanciani
The Google search engine will find you thousands of
additional links:
http://www.google.com/search?num=100&hl=en&newwindow=1&client=googlet&q=pantheon+rome&btnG=Google+Search
----------------
* In modern
concrete, the aggregate (usually small broken stone or gravel) is mixed
with the liquid cement before it is poured. Roman concrete was
laid differently: a layer of aggregate was laid down by hand and
pounded in, and then liquid cement was poured on top and rammed down
between the aggregate pieces. The process was repeated as many
times as necessary to achieve the desired depth. Aggrergate
pieces were typically larger than what is used today, the usual maximum
size being about four inches in diameter.
