The best-preserved Roman temple. The most impressive product of Roman engineering.
Arguably the most influential building of all time. As a monument, and as a relic of
the classical world, the Pantheon stands alone. Unlike so many great buildings, the Pantheon is
easily accessible. The doors are almost always open, and tourists stream steadily over the marble
floor, gaping at the famous dome. Most visitors stay only a few minutes, and even those who come
armed with guidebooks and the best of intentions often leave the building with only a vague idea of
the Pantheon’s history and significance. This video uses some of the Pantheon’s
often-overlooked details to explore that history and significance, and to explain why this most
famous of Roman buildings lives up to the hype. As usual, I’m Dr. Garrett Ryan;
and I hope you’ll enjoy this brief journey into the hidden history of Rome’s Pantheon.
I like to approach the Pantheon from the west, where a narrow street broadens
without warning into a piazza, and the temple looms abruptly overhead.
Before taking the obligatory pictures of the façade, I often circle the curving outer wall.
Although this rugged cliff of masonry isn’t as photogenic as the façade,
it’s every bit as impressive. For here, and only here, the bones of the Pantheon are visible.
The Pantheon is the supreme triumph of Roman concrete.
Roman concrete consisted of the volcanic ash known as Pozzolana, mixed with water and lime. It was
not poured like its modern counterpart, but laid like mortar in thin courses.
First, retaining walls of brick or stone were constructed as a sort of form.
A layer of coarse aggregate – usually chunks of limestone or broken tile – was laid down,
and the blend of pozzolana and lime was troweled over it, almost dry. The mixture
was then pounded firm with wooden mallets. The concrete foundations and walls of the
Pantheon were likely constructed by several contractors working in unison.
Each contractor employed a small team of masons, who built the brick facings. The blend of rubble
and concrete that made up the bulk of the wall was then laid by teams of unskilled laborers.
It seems to have been typical to finish about four feet (1.2 meters) a day.
The hard part, especially in buildings with very thick walls,
was ensuring that the concrete dried and settled evenly. To ensure that it would, the architect of
the Pantheon incorporated an elaborate series of chambers and recesses into the walls,
which introduced air into the masses of concrete and reduced the structure’s overall weight.
The voids in the Pantheon’s walls were spanned by relieving arches of brick, which evened
settlement of the concrete core and directed weight toward the rotunda’s strongest points.
Although the blind arches visible in the Pantheon’s brickwork seem to be structurally
distinct from the relieving arches in the concrete behind them, they fill the same basic function,
strengthening the mass of masonry and preventing the development of critical stresses.
Now, having stared at walls long enough, we come around to the front of the Pantheon.
As we see it now, the Pantheon looks like what it is: a relic from a vanished world.
It is surrounded by buildings nearly 2000 years younger than itself, and stands almost two stories
below the level of the surrounding streets. To understand its intended visual impact,
we have to imagine how it appeared in antiquity. Or, instead of imagining, we can just look at this
nifty reconstruction. Originally, the Pantheon stood at one end of a long colonnaded court.
It was elevated above the surrounding plaza, not sunk below it. And the dome,
now so prominent, was visible only as a flickering glint of gold above the porch.
It’s much more obvious now than it was in antiquity that the Pantheon consists
of two very different parts: the colonnaded portico and the concrete rotunda behind it.
The portico looked like the vast majority of Greek and Roman temples. The rotunda,
on the other hand, was almost unique – a typically Roman fusion of innovation and conservatism.
Since the Renaissance, visitors have noticed that the Pantheon’s portico and rotunda
are awkwardly joined. The portico seems too short for the huge building behind it.
And in fact, to judge from a second pediment outlined on the block
that connects it to the rotunda, the portico was meant to be ten feet higher.
This has led scholars to conclude that the Pantheon was supposed to have taller columns.
It may have failed to receive them because the columns were lost in transit
or diverted to another construction project. But it’s also possible that the sheer weight
of larger columns would have problematic on the marshy ground beneath the Pantheon.
The columns the Pantheon did receive are 40 Roman Feet tall – that’s the
equivalent of about 39 standard feet, or 12 meters – and weigh about 50 tons each.
Although their Corinthian capitals are marble, the columns themselves are Egyptian granite.
Unlike the Greeks, the Romans liked monolithic columns – columns carved, that is, from a single
piece of stone. Monolithic columns made of marble tend to crack along natural fault lines.
But granite, an igneous rock, has no natural faults, and can thus be used safely. All the
columns on the outside of the portico are gray granite, except for the three on the left,
or east, side. These three were imported from other Roman buildings
and installed in the seventeenth century to replace columns damaged during the middle ages.
The inscription on the Pantheon’s façade reads
“Marcus Agrippa, son of Lucius, being consul for the third time, built this.” Agrippa, however,
had nothing to do with the temple you see. He was responsible for the original Pantheon,
which was destroyed by fire and replaced by the current building early in the reign of Hadrian.
Hadrian left Agrippa’s name on the façade as a gesture of humility.
The later emperors Septimius Severus and Caracalla, however,
had no qualms about associating their names with a very minor restoration; you can just
barely see out the two-line inscription they left, just above the column capitals.
The triangular pediment of the Pantheon is just a wall of battered travertine now.
But during the Roman era, to judge from holes in the stone, it sported a colossal bronze eagle.
Until the seventeenth century, the Pantheon’s portico featured a ceiling of gilded bronze,
suspended from a unique system of tubular bronze girders. But in 1626,
Pope Urban VIII tore the girders and ceiling down.
The bronze, which weighed more than 450,000 pounds, was melted down and cast into 110 cannons
for the papal arsenal. The wooden rafters and roof we see today are 17th century replacements.
On either side of the Pantheon’s door are huge alcoves, which probably held colossal
statues of Augustus and Agrippa. Like much of the Pantheon’s exterior, they were originally veneered
with marble, which was stripped away and burned for lime sometime in the middle ages. These days,
the Pantheon’s glories are all inside the rotunda. And so, trembling with anticipation,
we approach the door. The bronze door we see today may not be original, since the marble frame,
40 Roman feet tall, was apparently designed for a much larger gate. But even if the door
we have isn’t original, it is ancient – one of the very few Roman doors still in service today.
So, let’s take a deep breath, pass over the marble threshold, and step into the greatest triumph
of Roman architecture. As we enter,
let’s do what everyone does, and look up.
The rotunda of the Pantheon is both awesomely spacious and impressively symmetrical. It has
a diameter of 150 Roman feet (that is, 142 standard feet, or 43 meters), uninterrupted
by any column or buttress. The crown of the dome is exactly 150 Roman feet above the floor.
As the illustration shows, a sphere 150 Roman Feet in diameter would fit perfectly inside,
just kissing the walls, floor, and dome. Since the initial impression created by the
rotunda is so overwhelming, it might be useful to identify a few of the details that make it so
special. Let’s start with the floor. Though repaired over the centuries, the Pantheon’s
floor is original. It contains a dazzling array of imported marble, granite, and porphyry, whose
differing colors and textures draw the eye along a checkerboard pattern of circles and squares.
The walls of the rotunda – nearly 20 feet, or 6 meters, thick – are interrupted by seven large
alcoves framed with columns of colored marble. Between the alcoves are marble
shrines built into the walls. Both alcoves and shrines were designed to frame statues
of the gods and emperors. They now house a series of chapels and devotional images.
Ever since the Byzantine emperor Phocas gave it to Pope Boniface IV in the early seventh century, the
Pantheon has been a church, consecrated to Mary and the martyrs. According to one medieval legend,
in fact, no fewer than 28 cartloads of martyrs’ bones were brought here from the catacombs
and placed beneath the altars. Although the Pantheon remains a church,
the fame of its relics has long since been eclipsed by the fame of its architecture. Since
the Renaissance, the building has been revered as both a miraculous survival from antiquity and as a
symbol of the city of Rome. These associations made the Pantheon the final resting place of
several Renaissance artists, including Raphael, and of the first two kings of unified Italy.
Now, at last, we look up from the alcoves and altars and dead artists,
and admire the famous dome, wider even than the dome of St. Peter’s Basilica,
Like the walls, the dome was built from layers of concrete,
molded and hammered over a gargantuan wooden form. To prevent the weight of the dome from pushing the
walls outward, the architect of the Pantheon made the dome heaviest and thickest around its edges.
The upper parts of the dome, on the other hand, were made as thin and light as possible,
partly by mixing feather-light volcanic scoria from the slopes of Vesuvius into the concrete.
The appearance of the dome was also carefully considered.
The five rows of recessed coffers have the practical function of reducing the dome’s weight.
But they are also integral to the visual impact of the building, creating a constantly shifting
visual drama as they catch and hold the light spilling in through the oculus. The effect would
have been more pronounced in antiquity, when the coffers were studded with gilded rosettes.
Besides the door, the oculus, or skylight, in the center of the dome
was the Pantheon’s only source of light. The oculus is 30 Roman feet (almost 9 meters) across.
Like the coffers, it had the function of reducing the dome’s weight. But again like the coffers,
it’s an integral part of the decoration – the brilliant focal point of the whole interior.
The oculus has never been glazed, and rain pours freely through it.
The water, caught by drains in the floor, flows out to the Tiber through the original Roman sewer.
If you look closely at the oculus, you can see an elaborate metal molding around the rim.
This is the only surviving component of the Pantheon’s original gilded bronze
roof. The rest of the bronze was stripped away for scrap in the early middle ages,
and replaced with the lead sheeting that still covers the dome.
Today, as mentioned, the Pantheon is a symbol and icon of Ancient and modern Rome. But what purpose
did it serve when it was first built? The name “Pantheon” suggests a temple to all the gods.
But it seems clear that the building was primarily designed for veneration of the Roman emperors,
in a setting that may have been intended to evoke the shape of the universe itself.
Before we leave the Pantheon, let’s pause by the door, and imagine what the building was like in
antiquity. Gods and emperors gaze out from the alcoves and shrines. The sharp aroma of incense
hangs in the air. Sunlight streams through the oculus, inscribing the pattern of the seasons
on the geometries of the floor. And overhead, the rosettes in the dome sparkle like stars.
I hope you enjoyed this short tour of the Pantheon. I plan to do other “hidden histories”
of famous ancient monuments in the near future, so stay tuned. If you have any suggestions for
buildings you’d like to see explored on this channel, please let me know in the comments.
For more on Roman concrete and Roman construction, check out my forthcoming book Naked Statues, Fat
Gladiators, and War Elephants: Frequently Asked Questions about the Ancient Greeks and Romans.
You can find many more free videos and fun details about the classical world on my website
toldinstone.com. In the meantime, as always, thanks for watching.