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EARLY HISTORY OF THE PANTHEON

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The huge columns of the Pantheon front entrance

INTRODUCTION

The Pantheon is the best-preserved Roman building that has survived for almost 2,000 years. It is also one of the most recognized symbols of the Roman Empire, surpassed only by the Colosseum. It was where ceremonies took place, and statues of all the major Roman gods, such as Jupiter, Saturn, and Mercury, were housed. Furthermore, the Pantheon got its name from the two Greek words PAN and THEOS, which mean "All Gods."

This ancient building is so unique and unlike most structures the Romans built. What makes it unique is its Rotunda, a large and high circular hall forming a cylinder covered by a huge concrete dome with a wide hole in its centre open to the bright sky and weather. And, yes, rain does indeed fall inside the Pantheon through this roof hole called an oculus.

The effect when one walks into the heart of this ancient building is stunning. The Pantheon truly showcases the brilliance of Roman engineering and imagination. Moreover, despite our modern technology and architecture today, the ancient dome of the Pantheon is still the world's largest unreinforced concrete dome. It is 43 metres wide (142 feet), which is the length of the Ha'Penny Bridge in Dublin, Ireland, or 90% of the height of the Arc de Triomphe in Paris, France. The photo below conveys the remarkable size and effect of this ancient dome.

The stunning Pantheon Dome and its Oculus open to the sky
Licensed from Alamy

FROM PAGAN TEMPLE TO CHRISTIAN CHURCH

For over 300 years, the Pantheon was a pagan temple dedicated to numerous Roman gods until such worship was banned in 391 AD by Emperor Theodosius. After the ban, the building then sat empty for 220 years until it was converted into a Christian Catholic church where religious services still take place today.

In the year 609 AD, Emperor Phocas of the Eastern Roman Empire ("Byzantine Empire") visited Rome, and he agreed to allow Pope Boniface IV to convert the Pantheon into a church. And thus, on May 13th, 613 AD, the former temple was consecrated as the Church of Sancta Maria ad Martyres (St. Mary and the Martyrs). The remains of many Christian martyrs were removed from catacombs and placed within the Pantheon. A myth says that, after the statues of the Roman Gods were carried out and smashed into pieces, a storm of demons was heard wailing and screeching as they fled upwards through the large hole in the top of the dome, known as the "oculus."

WHAT COULD HAVE BEEN

We are very fortunate the Pantheon survived because other Roman buildings similar to the Pantheon did not fare as well. For example, in the ruins of the Baths of Trajan in Rome, a similar structure can still be found. Just like the Pantheon, this ruined building is round and has the remains of a dome that is coffered on the inside. But this building did not survive - in the 21st century, it is mostly destroyed, as seen in the photo below. Barriers have been placed in front of the structure to protect what remains.

This could have been the Pantheon today
Pantheon-like building - Baths of Trajan, Rome
Image courtesy of AncientDigitalMaps - CC BY-NC 2.0

During its 1,900 years of existence, the Pantheon so easily could have been destroyed, especially after the fall of the Western Roman Empire in 476 AD. After the empire fell, there was no longer the organization nor the finances to repair damaged buildings.

For example, it could have been irreparably damaged if a terrible earthquake or fire had engulfed the Pantheon before it was converted into a church. And, if it had not been converted into a church that was regularly maintained and repaired at great expense over 1,400 years, the ruin shown in the photo above so easily could have been the Pantheon today.

A close examination of the photo shows many similarities to the Pantheon. For example, notice how the building is rounded and has niches in the wall where statues were housed. Also, the surviving part of the domed ceiling is coffered exactly like the Pantheon. Additionally, each coffer is made up of three successively smaller, recessed squares, just like the Pantheon's dome. And the ratio of the building is the same at 1 to 1 - height and width.

While the Pantheon, historically and architecturally, is an iconic building, it was not entirely unique in the Roman world. For example, the Baths of Diocletian had five structures covered with domes and an oculus (hole) in the centre, just like the Pantheon. And two of those structures have survived - one is now a church, and the other is now a museum that also had been a planetarium for several decades.

Emperor Trajan Built third Pantheon

Emperor Hadrian Built third Pantheon

Emperors Trajan and Hadrian built the Pantheon we see today, and the architect may have been Apollodorus of Damascus, but the actual designer is unknown. Most articles will state that only Emperor Hadrian was the builder and patron of the Pantheon, but I will explain why this is probably incorrect.

The Romans put datestamps on all the bricks they made, and recent research shows that most of the Pantheon's bricks date from the early 110s AD. Therefore, some of the brickwork was done during the reign of Trajan, who ruled before Hadrian from 98 to 117 AD.

In my personal opinion, because Emperor Trajan died almost ten years before the Pantheon was completed, Emperor Hadrian must have been heavily involved for several years in the construction of the Pantheon, which is a testimony to his vision and genius as a Roman emperor who built many great buildings.

Furthermore, Hadrian likely suggested many architectural and design refinements to the structure. For example, the colouration and design elements of the dome's ceiling, the colour and pattern of the floor tiles, the choice of statues, and the interior wall panel and decorations very likely were all selected by Hadrian. However, it cannot be denied that Emperor Trajan also was involved in the early planning and construction, as suggested by the datestamps upon the Pantheon's bricks. Thus, I believe it is reasonable to say that the Pantheon we behold today in the 21st century was built by two emperors, cousins to each other.

The quote below, and this chart of brick samples from the Pantheon, give good insight as to who began the construction of the Pantheon building we see today (there were two previous versions of the building that were both destroyed by fire).

Dated brickstamps give scant support for the claim that the emperor Hadrian was either its patron or its designer. There is no reason not to take the Trajanic brickstamps found in the Pantheon at face value.

Lise M. Hetland, Three New Perspectives on the Dating of the Pantheon

There are several dates given for when the Pantheon was completed. The dates 125 and 126 AD are often quoted, but my research indicates that the Pantheon was built over a period of approximately 15 years, starting in 111-113 AD/CE and ending in 128 AD

The dates are uncertain because precise information regarding the Pantheon has not survived the 2,000 year jouney into the 21st century. Therefore, historians have to play detective and make educated guesses based on archaeological research, ancient document research, and some enlightened speculation. This is also why data can differ depending on what article you read.

Marcus Agrippa Built first Pantheon

Emperor Domitian Rebuilt Pantheon

The Pantheon we see today is not the original structure - it is the third. The first Pantheon was built in 27 BCE by Marcus Agrippa, son-in-law to Emperor Augustus, and an architect and military General. He built the Pantheon to commemorate both his and Emperor Augustus' great naval victory at Actium, that gained victory over Marc Antony and Cleopatra four years earlier in 31 BC. Agrippa commanded the naval forces during that battle and thus played a pivotal role in a victory that cemented Augustus as the undisputed leader of the whole Roman world. Note: During that time, Augustus was known by the name Octavian.

What did the first Pantheon built in 27 BC, 150 years before the third version, look like? The best and probably most correct answer to that question comes from Wikipedia, from which I quote:

The form of Agrippa's Pantheon is debated. As a result of excavations in the late 19th century, archaeologist Rodolfo Lanciani concluded that Agrippa's Pantheon was oriented so that it faced south, in contrast with the current layout that faces north, and that it had a shortened T-shaped plan with the entrance at the base of the "T."

Agrippa's version of the Pantheon was built over 150 years before the 128 AD building we see today. In my opinion, people who claim the Pantheon we see today is just a copy of the first building are incorrect. The current Pantheon's unique design was a type of Roman architecture that did not exist 150 years earlier in Roman civilization. A further section below explains the evolution of domes with a hole in their centre (oculus), which began around 50 AD.

The 27 BC building predates the evolution of dome-with-an-oculus architecture by almost a century. Also, when Trajan and then Hadrian were building the third version of the Pantheon, a new, circular foundation had to be built. Thus, Agrippa's version did not already have a round foundation, indicating a rectangular structure. This first version of the Pantheon was destroyed by fire in 80 AD, 107 years after its completion in 27 BC.

The second Pantheon was repaired and rebuilt by Emperor Domitian. Unfortunately, just thirty years later, this second version of the building was hit by lightning and again destroyed by fire in the year 110 AD. Because the Romans believed their gods caused lightning, they may well have thought their deities were not pleased by the Pantheon, thus requiring rebuilds. Interestingly, Romans would watch the southern skies; if a lightning bolt travelled east to west, that was a good sign. However, if the bolt travelled west to east, that meant trouble, usually political.

Finally, the third Pantheon, which we see today, was started by Emperor Trajan and completed by Emperor Hadrian from approximately 111-113 to 128 AD. So yes, the story of the Pantheon is a bit complicated.

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THE PANTHEON EXTERIOR - THEN AND NOW

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THEN ... The Pantheon exterior in 128 AD
Image from Ball State University, IDIA Lab

Notice how the image above shows a Pantheon with a staircase in front that went down to a ground level much lower than now. Additionally, you can see a large bronze eagle inside a wreath and ribbons drifting towards the corners in the tympanum area below the entrance roof. There were also two giant statues representing Emperor Augustus and Marcus Agrippa, one on either side of the main entrance. These statues stood inside large wall niches.

Finally, you can see how the granite columns differed in colour. This is because it was common for Romans to apply paint to columns in ancient times.

These 16 solid granite columns are 12 metres high (40 feet) and weigh 54 metric tons each (60 US tons). These massive columns were produced in the Mons Claudianus quarries of Egypt, where they were then dragged to the Nile river, placed on barges and shipped 2,000 km (1250 miles) to Rome. Imagine the tremendous amount of labour and expense involved in creating and then transporting so many columns of this size so far.

The Corinthian capitals on top of each column are made from white Pentelic marble from Greece - the same marble used to build the Parthenon Temple in Athens, Greece.

NOW ... The Pantheon exterior in 2020
Image courtesy of Paulo Ricardo Carrara - April 2020

In the photo above, notice how the lower part of the columns is dark and discoloured compared to the upper part - caused by 15 centuries of contact with mud and debris and floods - this gives one an idea of how high the ground used to be. In fact, during the Middle Ages, the ground surrounding the Pantheon was so high that people actually had to descend seven steps down to reach the Pantheon's front entrance; I explore this subject in greater detail, with images further down.

In the 21st century, the ground is now almost level with the Pantheon floor. And the stairs in front of the temple, made of beautiful yellow Giallo Antico marble, are now buried.

During the Middle Ages and Renaissance eras, the Piazza della Rotonda was famous for being the home of delicatessen shops and numerous stalls specializing in the sale of cured meats, sausages, cheeses, eggs, and anchovies. These merchants were known as pizzicagnoli.

By the end of the 1700s, this market facing the Pantheon was known for the variety of birds and cages on display in addition to food stalls selling vegetables, fruit, flowers, sausages, and cakes. But, unfortunately, it was also famous for the stench and filthy, sticky muck covering the surface of the square, in addition to hordes of beggars and plentiful purse-snatchers.

The open square seen today, known as the Piazza della Rotonda, came about only after a long struggle that lasted hundreds of years. In the early 1800s, Pope Pius VII ordered the demolition of many sheds, stalls, shops, inns, and taverns that filled the square with filth and odours. The square in front of the Pantheon then began to resemble what we see in the 21st century. However, the vendors had a habit of returning for several more decades and flaunting prohibitions.

This loud and busy marketplace was finally brought under control during the 1870s by Pope Pius IX (1846-1878) when vendors were relentlessly banned, and buildings adjacent to the Pantheon were demolished - this was the culmination of a long process initiated by various Popes. Interestingly, when French troops occupied Rome from 1808 to 1813, Napoleon Bonaparte wanted many of the buildings filling the Piazza della Rotonda destroyed. However, Napoleon's plan for the square never came about during the five years of French occupation. If his plan had been enacted, the square could have been cleared decades earlier.

The Piazza della Rotonda marketplace in the early 1500s

My drawing above shows how the square and the Pantheon may have looked in the early 1500s. At this point in history, the Pantheon had only one bell tower, and the ground in front was not yet lowered. Also, the portico was not yet restored, the large fountain did not exist, and the marketplace was not regulated or pushed back from the Pantheon. Basically, the area surrounding the building was a filthy, crowded, and chaotic mess.

In Roman times, the brownish brick on the outside of the Pantheon was covered with white Pentelic marble panels, traces of which are shown in the image below. Today, the white marble is in poor condition and discoloured, but it must have looked very impressive long ago.

Marble veneer still covering part of a Pantheon wall

These few remaining slabs of marble veneer suggest how the Pantheon exterior looked when all the ancient brickwork was covered. However, not all of the outside walls were covered with marble. Instead, most of the Pantheon's exterior was covered with a white stucco due to the steep expense and labour involved with marble veneers.

The stucco was made from lime powder and was easily molded onto walls. On the exterior of buildings, it was fashioned to imitate white marble blocks, thus producing a bright and attractive surface. Additionally, Travertine stone, a cheaper alternative to marble, was often used in combination with stucco to create specific architectural details and decoration.

Most of the Corinthian capitals on top of the columns have been worn down, except for three columns on the extreme left side, whose Corinthian capitals are in good condition. Those three columns, however, are not the original ones - they are replacements. Two of the columns came from the nearby Baths of Nero in 1666 AD, while the third came from Domitian's Villa located in Castel Gandolfo outside Rome in 1626 AD.

And though the huge bronze eagle and wreath located in the tympanum are gone, experts can estimate their existence because of the pattern of holes formed by metal pins that attached the eagle and wreath to the structure's surface. Also, golden roof tiles, made of gilded bronze, covered the Pantheon's wide dome and entrance roof (Portico). The outside appearance of the Pantheon in 128 AD was certainly far brighter and shinier than it is today.

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THE PANTHEON INTERIOR - THEN AND NOW

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THEN ... Pantheon interior in 128 AD
My remastered version of Ball State University IDIA Lab image

The image above shows the original Pantheon interior created in 128 AD. The statues are all Roman gods, such as Jupiter, Venus, and Mercury. The dome is painted, and its ceiling is lined with lead with coffers highlighted in bronze. The large fluted columns are marble and have Corinthian capitals. The wall area with "windows" above the columns is called the Attic, which is made from marble and porphyry stone. The floor's pattern and colours have not changed. So when you enter the Pantheon, you are seeing the floor as the Romans saw it.

NOW ... The Pantheon Interior in 2021
Licensed from Dreamstime.com

On the surface, the Pantheon still looks much the same in the 21st century. However, after 1,900 years, it is not surprising that much of the Pantheon's interior has actually been replaced and resurfaced. For example, from 1757 to 1759, the Attic was replaced with a new pattern and materials by Paolo Posi. The original materials crumbled when removed for cleaning and could not be reused. In tribute to the ancient design, a small section of the Attic (upper right) retains the original pattern but is made from newer materials. To see what the Pantheon looked like in 1747 with its original Attic dating from 128 AD, click this link.

The dome is now bare concrete, and the original Roman statues were removed, destroyed, and replaced with statues of Catholic saints. In addition, the niches containing statues have been reconstructed, and some of the columns have been replaced. Finally, many of the marble panels covering the walls had to be replaced due to centuries of flooding, mould, and humidity that discoloured and damaged the marble.

As mentioned earlier, the Pantheon floor seen today has the same ancient pattern and colour schemes, but most of the floor is not ancient. Approximately two-thirds of the floor was either replaced, resurfaced, or relaid in 1873. The walls are 6 metres thick (20 feet) to support the weight of the immense concrete dome. Furthermore, a series of brick arches, one beside the other, are embedded in the walls to help support and stabilize the overall structure.

Because the Pantheon's width and height are the same at 43.5 meters (143 feet), you could put a giant sphere inside the structure, and it would fit perfectly. These dimensions are not a coincidence - the Romans planned it that way. So much planning and thought went into the creation of the Pantheon.

Dome and attic converge above the entrance - a perfect fit !

- Image courtesy of University of London - Warburg Institute

The large columns, made of a yellowish marble with red veins known as "Giallo Antico," are still the original ones. You can see a closeup of these columns below - notice the red veins inside the yellowish marble. The pristine condition of the Corinthian capitals and the fluted columns is impressive.

These columns and the lower wall panels were once covered in filth until, one day, in 1705, someone cleaned a section of a column beside Raphael's tomb, revealing the beautiful and shining marble under the accumulated dirt.

Closeup of Pantheon's Giallo Antico marble columns

Pope Clement XI Albani and several Cardinals rushed to the Pantheon to see the amazing, cleaned column. Upon arriving, they were so impressed that the Pope authorized work to clean, right up to the cornice, the whole interior of the Pantheon rotunda. The work took six years, ending in 1711, at great expense. The regular flooding had also affected the floors, causing some floor stones to be displaced and promoting the growth of vegetation inside due to the build-up of sediment.

Pantheon in 1530s - only 7 columns in front - Part of the tympanum is missing - Only one central bell tower above portico - A Chapter House building was attached to Pantheon's east side. Sketch by Maerten Van Heemskerck

The Pantheon's current good condition required centuries of substantial restoration and cleaning. For example, the whole Attic section above the columns was rebuilt, as were most of the niches holding large statues. Also, the floor was restored and relaid in 1873, and the ground level of the plaza in front of the Pantheon was lowered by over 6 metres (20 feet) - still a few metres above the original 128 AD ground level.

In the 1800s, many adjacent and nearby structures associated with the former marketplace in the Piazza della Rotonda were demolished. The wide-open square in front of the Pantheon in the 21st century is the result of much digging, demolition, and law enforcement since the 1700s.

For centuries, the eastern side of the portico was missing three columns and a section of the entablature and tympanum above those missing columns. This damage was repaired over a period of about forty years, from 1626 to 1666 AD. The following quote expresses well the extent of Pantheon interior restorations (note: revetment means surfacing material):

It is important to remember that the Pantheon presents today's visitor with a mixture of ancient materials and modern repairs and replacements. Some of these interventions are easy to identify, such as the coffering and other embellishments in the principal apse and of course any feature related to Christianity.

In other cases, the ancient elements and their subsequent replications are less easy to distinguish.

Detailed inspections and technical analysis during a campaign of conservation under the direction of Mario Lolli Ghetti in the 1990s have revealed the full extent of the renovations of the seventeenth and eighteenth centuries, when a substantial proportion of the ancient revetment was replaced with thinner sheets of marble (often reworked ancient material) bonded to backing slabs of coarser stones.

The Pantheon: From Antiquity to the Present, page 1, Cambridge Univ. Press, 2015

The main point the author is making is that the Pantheon in our century is a blend of ancient and new. While the core structure is ancient, the other parts, such as the marble wall panels and many floor sections, had to be replaced due to deterioration over 1,900 years. Furthermore, new materials were not always used. Instead, when possible, original parts were resurfaced and reused in the restoration. Two images below show the Pantheon exterior in the 1600s. Touch or move the cursor over the image to see another view.

The images above from 1667 show a Pantheon portico free of the old Chapter House that caused the loss of three columns and the entablature above them. By that year, the missing three columns and upper structure on the left side were replaced so that the Portico once again had eight columns along the front. In addition, from 1662 to 1666, Pope Alexander VII had the area in front of the Pantheon lowered to just below the portico floor level.

Interestingly, though the original Chapter House was demolished, both images show that another building, built further back from the Portico, was directly attached to the eastern side of the Pantheon. This happened in the 1660s when they restored the three columns and repaired the entablature and pediment. And also, notice how two new bell towers have replaced the single tower added in the year 1270 that stood for almost 400 years.

The people of Rome hated the two bell towers, referring to them as "the asses ears." They were not designed by Bernini, as commonly believed. The towers stood above the Pantheon for over 200 years until they were finally removed in 1883.

The whole process of restoring the Pantheon has been a very long evolution. Fortunately, today, we again have a Pantheon that stands alone and is no longer encumbered by other structures. It is finally restored to the status it originally had in 128 AD. Perhaps, someday, they will also lower the ground surrounding the Pantheon even more so that it can once again sit upon a podium reached by that wonderful Giallo Antico marble five-step staircase.

Interestingly, in ancient times, the whole area in front of the Pantheon was paved with Travertine marble slabs which are still there, preserved by a layer of silicate-based material called pozzolan. The slabs are located 2.4 metres (8 feet) below the current ground level in front of the Pantheon, and they date from approximately 25 BC. These slabs were placed there under the direction of Marcus Agrippa when he built the first version of the Pantheon. These slabs show that the ground-level of the large Piazza della Rotonda square in front of the Pantheon is still a few metres above the original 128 AD ground level.

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THE CHANGING PANTHEON GROUND LEVEL

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Pantheon's changing ground levels over 1,900 years

The Pantheon was built in a section of Rome called the Campus Martius (Field of Mars). Because of its location, this part of the city was a floodplain prone to regular floods from the nearby river Tiber which deposited layer after layer of sediment. During Roman times, the flooding was controlled, but after the fall of the Western Roman Empire in 476 AD, things changed for the worse.

As the centuries went by, the ground level of the Campus Martius area steadily rose as layers of sediment from flooding were deposited. Additionally, over the centuries, garbage piled up from the people living in the Campus Martius area of Rome. Another factor leading to the rising ground level was the sheer amount of stone and brick debris from all the crumbling ruins in the area.

As the ground surrounding the Pantheon rose over 8 metres (26 feet), the Pantheon floor level sank further and further below the ground level of the surrounding city. Understandably, this had a terrible effect on the Pantheon's internal water drainage system. For example, every time the nearby Tiber river flooded, water from the river rushed through the sewer system and entered the Pantheon through the main floor drain below the dome's oculus.

As a result, you can imagine the damage to both the Pantheon floor and the entire lower area of the Pantheon, such as the columns, statue niches, and marble wall panels. Those parts of the Pantheon all became covered in debris, mould, and slime - and sections of the floor were displaced, discoloured, and ruined.

As mentioned earlier, from 1662 to 1666, the ground level of the Piazza della Rotonda square in front of the Pantheon was lowered to just below the temple's portico floor level. While this was an improvement, it still left part of the Pantheon's structure and front staircase below the ground. So why did they not dig deeper?

Initially, Pope Alexander VII wanted to lower the ground to the ancient 128 AD level, but it was too expensive. Furthermore, it would have caused many problems for all the surrounding buildings and sewer lines, as explained in the quote below:

To bring the piazza down to its ancient level would have required reburying sewer lines; moreover, new sets of stairs would be necessary in front of every building around the piazza, and they would have intruded on the liberated space. Surrounding streets would have required stepped or ramped access points. For all of these reasons, the pope’s ambitions had to be reconsidered.

Tod. A. Marder; "The Pantheon - From Antiquity to the Present

In conclusion, a plaza lowered to the original 128 AD ground level would have created a large, rectangular "pit" that disrupted all the connecting streets and buildings. All those structures and thoroughfares would have required staircases or inclined slopes, an effect that probably would have looked unpleasant. In my opinion, judging by how the Piazza della Rotonda looks today, they made the right decision in the 1660s.

Between 1532 and 1537 AD, Maerten van Heemskerck, a Dutch artist living in Rome, made very accurate sketches of the ancient ruins and works of art. One of his sketches (below) is of the Pantheon Portico, showing a staircase (image left side) that descends from a ground level almost one-third of a column higher than the Portico floor. The viewpoint is from the right side (west) of the Portico, and the artist is looking across to the other side, which is blocked with a wall. The large bronze door entrance to the Pantheon is on the right.

Pantheon portico with a staircase in the 1530s
Sketch by Maerten von Heemskerck- 1498-1574

Let us now contrast the sunken Pantheon portico of the 1530s with the portico ground level of today in the 21st century, as shown in the video below.

Looking west to east thru Pantheon Portico and then to the front

In the video above, just like the Van Heemskerck image from 1530s, the viewpoint is west to east through the portico. The camera then wanders towards the two central columns where indentations from the attached staircase are still seen - this shows how high the ground was.

In the 21st century, the portico floor has been restored, and the ground is now just slightly lower than the Pantheon portico floor. Also, as shown in the video, none of the columns have walls between them. Additionally, the former Chapter House structure (for the Canons of Santa Maria ad Marytyres church) built onto the east side of the portico is now long gone.

Notice also how, in the line of front columns, the farthest column on the right is reddish-pink in colour and not whitish like the others. That corner column is one of the three replacement columns installed in 1626 and 1666 AD. These replacements came from the nearby Baths of Nero/Alexander and Domitian's Villa in Castle Gandolfo.

Image showing how the ground rises along sides of Pantheon.
Ground is level with the Pantheon Portico in the front only
Image Courtesy of Google Earth

The recent image above shows how the streets on either side of the Pantheon slope upwards from the front to the rear of the Pantheon. The ground in front of the Pantheon is now level with the Portico floor; however, in the Middle Ages, the ground in front was just as high as the rear. Without modern equipment, it must have required a tremendous amount of laborious digging and carts to reduce the dirt and debris in front of the building by several metres/yards.

The process of earnestly removing buildings and the debris that had accumulated up to the Middle Ages was begun by Pope Eugene IV (1431-1439). With his interventions, the Piazza della Rotonda square facing the Pantheon attained new boundaries and was paved, but the ground was not lowered. Basically, he tidied things up quite a bit.

The person responsible for clearing most of the square's former marketplace and adjoining structures in the 1700s, after the ground was lowered in the previous century, was Pope Pius VII. He had the marketplace transferred to the Piazza della Coppelle and ordered many demolitions.

High on a wall at the north end of the Piazza della Rotonda facing the Pantheon is a white marble plaque (click to view) commemorating Pope Pius VII's efforts. For example, the plaque states how this Pope "demolished the vile taverns." Pope Pius IX, in the mid-1800s, demolished even more structures, resulting in the city square we see before the Pantheon.

Sixty years before the Pantheon was completed, another concrete dome with an oculus was built in 68 AD. This dome still exists within the ruins of the Domus Aurea ("Golden House"), a 300-room palace built by Emperor Nero. The image below shows the eight-sided "Octagonal Hall" with its dome and oculus in the Domus Aurea. The alternating images will show how the room looks now and then how it looked in 68 AD. People have speculated that this dome, just like the Pantheon, had an astronomical purpose or significance, in addition to its pleasing aesthetic properties and obvious purpose of providing light to the structure's interior.

The second example of a building with a dome and oculus is the Temple of Mercury, located in Baiae near Naples, Italy. This city was where many rich, ancient Romans lived in splendid villas by the sea before the ground shifted, lowering much of Baiae into the water. The Temple of Mercury was a Roman bath and not a temple. It was built around 50 AD, about seventy years before the Pantheon. The inside of this structure is now filled with water, and light enters the structure through an oculus opening at the top centre of a 22-metre wide (72 feet) dome.

Temple of Mercury in Baiae, Italy
Image courtesy of Google Earth

The final example of a Roman dome with an oculus is found in the Caldarium room of the Forum Baths in Pompeii. In this example, a dome with an oculus was used to illuminate the water-filled marble Labrum (see image below). Despite the relatively small size of the room, the overall effect is lovely and so practical in how it helps to illuminate the area. There are additional ceiling "sky lights" in the room, also.

Dome and oculus in the Pompeii Forum Baths
Photo Mary Harrsch - CC BY-SA-2.0

These three examples of Roman structures built with a dome and oculus decades before the Pantheon show how this architectural concept was not unique to the Pantheon. In fact, this was an evolving architectural concept used repeatedly along the path towards reaching its zenith in 128 AD with the completion of the Pantheon in Rome by Emperor Hadrian.

As you are now aware, the Pantheon's dome and oculus concept was not unique. Nevertheless, the Pantheon's vast and refined dome, with its impressive coffered ceiling and correspondingly enormous oculus, is far more stunning than the other architectural examples shown above. The ancient Romans' beautiful dome and oculus architecture, shown in the Pantheon video below, has had a profound effect on architecture.

In the image below, along the top edge of the Pantheon's oculus, part of the ancient copper plating that encircles the oculus only can actually be seen. The gilded bronze tiles that once covered the entire dome were removed by the infamous Constans II in 663 AD.

People standing beside the Pantheon Oculus in 1970s. Most are not standing because a sudden rush of air down into the oculus can hurl people to their death below.

Seventy-two years after the bronze tiles were removed, the dome was covered in lead plating by Pope Gregory III in 735 AD. Moreover, to this day, the dome is still covered in lead plates thanks to maintenance financed by many Popes over the centuries, such as Martin V, Eugene IV, Nicholas V, Pius II, and Clement VII.

Lead plating and rivets of the Pantheon dome roof
Image courtesy of Frank Baker Holmes 1975

After the original bronze roof tiles were removed, the Pantheon dome was left bare and exposed to the weather for over seventy years (633-735 AD) before lead plating was installed. But the seven decades of exposure did not actually cause any damage to the Pantheon's structures.

Fortunately, the concrete dome's surface is covered with a 15 cm depth (6 inches) of pozzolana cement that is very resistant to water. Furthermore, below the cement, the Romans embedded hidden tiles onto the concrete roof of the dome. The combination of pozzolana and tiles protected the dome from the effects of rain and the Sun.

Despite the Pantheon dome's resistance to the elements, it would be in bad shape today if it had been left bare since 633 AD, almost 1400 years ago. Undoubtedly, it was a wise decision to recover the Pantheon roof with lead plating.

Pantheon roof lead plating and stairs
Image courtesy of Frank Baker Holmes 1975

Several times I have read articles saying that the Pantheon dome was covered by two metal layers: an upper layer of bronze tiles with a second layer of copper plating below the tiles that Pope Urban VIII removed in the early 1600s. Any such statement is not accurate.

After Constans II removed the bronze tiles a thousand years earlier in 663 AD, the Pantheon dome roof was thus made bare, which was why Pope Gregory III had to cover the roof with lead. Why would he have covered the dome with lead if it was already plated with copper?

Also, in the 1620s, when Pope Urban VIII removed the Pantheon's bronze roof trusses from the portico, that was the only metal he took. There was no copper roof plating for him to take. If he had, it would have meant the copper was located beneath the lead plating installed in 735 AD. The labour and cost of removing tons of lead plating to retrieve copper and then replating the roof with sheets of lead again afterwards make no sense.

Astonishingly, the Pantheon floor is convex, meaning it slopes up from the sides towards the centre, the highest point of the circular floor. The actual convex slope of the floor as it rises towards the center is very slight and imperceptible. There are 22 drainage holes, two of which are located directly below the oculus. The other holes are located halfway between the centre and the interior wall. An image of the Pantheon's floor drains is shown below - notice the four drainage holes carved into the large marble tile.

The Pantheon Floor showing 4 of the 22 holes
Image courtesy of Creative Commons WKnight94

The image below shows the Pantheon with part of the floor surface removed so that you can see the drainage system below the floor slabs. There is a drain directly below the oculus, and you can see draining paths coming from the sides of the floor and towards the central drain. The central drain leads outside the walls and into a complex sewer system.

Based on a model of the Pantheon by Georges Chedanne (1861-1940)

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A PANTHEON RAIN OF ROSE PETALS

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Firefighters throwing rose petals into the Pantheon Oculus on Pentecost

Every year on Pentecost day, also known as Whitsun, firefighters on top of the Pantheon dome sprinkle thousands of rose petals into the oculus to the delight of the people below observing this beautiful red shower descend slowly to the Pantheon floor. In the photo below, these brave firefighters have climbed all the way up to the rooftop; however, they are not standing because a sudden wind gust down into the gaping oculus could plunge them to their death upon the Pantheon floor below.

Pentecost Sunday in the Pantheon - A Shower of Rose Petals
Saint Joseph @Flickr- CC BY NC ND 2.0

Pentecost is a Christian holiday that commemorates the descent of the Holy Spirit upon Jesus Christ's disciples and other believers gathered in Jerusalem for the Jewish Feast of Shavuot. This event caused the followers to speak in other languages while small flames appeared over their heads.

In Western Christian Churches, Pentecost falls on the 50th day (or the 7th Sunday) after Easter. The red rose petals symbolize hope and the tongues of flame seen above people's heads. If you want to attend the falling of the rose petals, get to the Pantheon early before the church service begins.

Pantheon floor covered with rose petals on Pentecost
SeleniaMorgilla @Flickr CC BY NC ND 2.0

As seen in the photo above, all the rose petals have fallen to the Pantheon floor - a wonderful sight and the fragrance coming from all thoses petals must be delightful. I do feel sorry for the poor people having to sweep the floors afterwards. Thank you to Selenia for the great photo.

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THE PANTHEON FOUNTAIN

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The fountain in front of the Pantheon in 1751 AD

Engraving/Sketch by by Giovanni Batista Piranisi (1720-1778)

Anyone who sees the Pantheon, either by visiting or through photos, will undoubtedly notice a large and ornate fountain in the square facing the ancient building. This fountain is known as the Fonta del Pantheon. The fountain we see today came about after many changes over 311 years, as explained in the timeline below:

	In 1575, Pope Gregory XIII wanted a large fountain in front of the Pantheon, and so it was designed by Giacomo della Porta. The marble work was done by Leonardo Sormani;
	In 1711, the tall obelisk we see today was added by Filipo Bargioni, who also made several changes to the original fountain by adding a new basin and changing aspects of its layout, as requested by Pope Clement XI;
	In 1886, the marble figures of the fountain were removed, and new ones were created by Luigi Amici.

The fountain is now almost 450 years old. The water is supplied by the "Acqua Virgine," rebuilt by Pope Nicholas V in 1453. It was formerly known as the ancient Roman aqueduct Acqua Virgo, built by Marcus Agrippa. The Acqua Virgine supplies both the Pantheon fountain and the famous Trevi Fountain in Rome.

The obelisk on top of the fountain was created during the long reign of Pharaoh Ramses II (1303-1213 BC) in Heliopolis, Egypt. It was brought to Rome by Roman soldiers, where it became part of the temple of Isis and Serapis devoted to the Egyptian goddess Isis. The nearby temple was located just east of the Pantheon. This obelisk is made of granite and covered with Egyptian hieroglyphs. Additionally, above the obelisk, the cross and symbols of Pope Clement XI were added.