The 18th-century Grand Tour must have been exciting time for young patricians seeking to discover the ancient world first hand in Rome. If they could put aside the temptations of pleasurable diversions, then serious learning and procuring a collection were attainable. One of the highlights for them must have been the Pantheon in Rome. A building surviving from ancient Rome with sound architecture, design, materials, and ornamentation. Studying it in the Renaissance gave Brunelleschi the information to build the magnificent dome of Florence Cathedral. A feat that seemed impossible at the time. Back home in England country house patrons and their architects could take inspiration for their own building works.

The Pantheon is a spectacular building which must have been even more spectacular back in AD 125 when Hadrian rebuilt it. It was clad with gleaming marble and stucco. I was struck by the fact that each age has its approach to analysis and reading of ancient buildings. Brunelleschi was looking for answers to overcome the engineering problems of creating a large dome. The 18th-century Grand Tourists were perhaps looking for an education in what constitutes both classical and good taste and their architects were thinking of how they can design and build for their patrons. These approaches require breaking down the elements of building, engineering, design, function, fabric, and ornament. In the late 21st century there are even more analytical approaches with advances in archaeological technology and techniques.

The previous temple on the site was built on the edge of the Field of Mars by Marcus Agrippa (c. 63 BC – 12 BC) in 27-25 BC. It burned down in AD 80 and was rebuilt by Domitian (AD 51 – AD 96, emperor AD 81 – AD 96). It was again badly damaged in AD 110. Hadrian (AD 76 – AD 138, emperor AD 117 – AD 138), the ‘building emperor’ as I like to call him, rebuilt it circa AD 118-25 and retained the inscription relating to Agrippa.

The inscription on the Pantheon portico reads: M. AGGRIPA L. F. COS TERTIUM FECIT

It translates Marcus Agrippa, son of Lucius, thrice consul, made this.[i] The pediment likely originally had gilded bronze applique set into it. The pattern of the holes that remain suggest an eagle with a wreath. The eagle and wreath are the attributes of Imperial Jupiter.[ii]

The Pantheon still is a wonder of Roman architecture, design, and engineering. Tourists in the 18th century would have been in awe of it as those in the 21st century. Over to the right in the photo above is the dome of St. Peter’s. Michelangelo took inspiration from the Pantheon and Brunelleschi’s dome in Florence for St Peter’s.

Dome of St. Peter’s Basilica

A ‘view’ painting of c.1734 by Giovanni Paolo Panini (1681 – 1765) gives an idea of the tourists of the time. Panini was both a painter and architect based in Rome. It shows people as they wander about today, some chatting, and others admiring. There are some that seem to be kneeling in front of Raphael’s tomb.

Source: Wikimedia Commons. Interior of the Pantheon by Giovanni Paolo Panini (1691-1765), c. 1734. In the collection of the National Gallery of Art, Washington.[iii]

The sunlight through the oculus appears in one position and will possibly move as it rises in the sky. The Pantheon faces north, facing towards Augustus’s mausoleum (63 BC – AD 14, emperor 27 BC – AD 14). The city buildings are now in the way. Hadrian had intended both the connection to the gods and to the emperor Augustus. Roman government and religion were closely tied. Keeping Marcus Agrippa’s name on the building also linked back to the time of Augustus and dominance of the Roman Empire.[iv] The spotlight from the oculus in the painting is just off the entrance, perhaps reflecting that the sun is in the south but has passed its zenith of the day, and it is not high summer (where perhaps the spotlight would be on the floor), maybe alluding to the passing of the Roman Empire.

The painting shows the inside of the Patheon looking back out towards the entrance. Unfortunately, I didn’t take a photo looking that way. However, below is the photo I took from the doorway. Little appears to have changed – this wonder of the ancient Roman world has intrigued many generations. We are seeing not just an interior surviving from the early 18th century but one that has survived from the AD 125. Although to keep up the interior it has been renovated and there are various burials of later centuries, as well as being converted to a church. But overall, we can get a wonderful insight into Classical Rome.

THE PANTHEON DOME – A perfect half-sphere

The exterior of the dome consists of concentric circles of Roman concrete are stepped from the base of the dome and get thinner towards the apex. The there is a ribbed cap supported by the concentric circles.

Relieving arches can be seen in the construction. The dome has a diameter of 43.2m (142ft) and was unsurpassed in scale until Filippo Brunelleschi (1377-1446) built his dome over il Duomo in Florence (built 1420 to 1446). Brunelleschi had spent time measuring ancient ruins in Rome and the Pantheon dome would have been an amazing inspiration for him. He copied the technique from the Pantheon of building up the solid inner shell with courses of Roman bricks set in a herringbone arrangement. The diameter of Brunelleschi’s dome was 46m (nearly 150ft).[v] However, the Pantheon dome is still the largest non-reinforced concrete structure in the world. Vitruvius would have approved. Brunelleschi had used hidden chains to reinforce his dome.[vi]

Florence Cathedral: Cathedral of Saint Mary of the Flower

Dome of Florence Cathedral

The engineering marvel of the Pantheon dome used a temporary wooden structure over which was poured concrete. Roman concrete (opus caementicium) was made of burned (or quick) lime and pozzolana (derived from volcanic ash) with an aggregate of pumice, stones, pebbles, sand, gravel, and rubble. With the decline of the Roman Empire later, so went the recipe and skill for making concrete. It wasn’t until circa 1756 in England that the civil engineer John Smeaton (1724-1792) pioneered the application of hydraulic lime in concrete with aggregate.[vii]

The diameter of the dome and the height are the same – 43.3 m (or 142 ft).[viii]

The ceiling coffers reduce in size around the dome towards the oculus. The function of coffers is to lessen and distribute the weight of the dome. The Ancient Greeks had previously developed the technique. Coffering became a significant theme in the Renaissance, the Baroque, and the neo-classical. In the country house back in England coffers offered that practical and ornamental use to show off one’s classical taste and make a statement. For example, the grand hall at Holkham House in Norfolk.

Holkham Hall Hallway – Holkham foundation stone laid 1734 and completed 1764


The Pantheon was made into a Catholic Church in AD 609 by Pope Boniface IV (Basilica of St. Mary & the Martyrs). Boniface removed the pagan ornamentation and statues. The exterior decoration has been mainly stripped over the years. Although the interior marble scheme has survived, with renovations, attempting to keep the scheme, over the years,[ix]

Becoming a church with the addition of significant burials of elite individuals and Raphael has kept a focus on making sure the interior is looked after.


The portico is held up by 24 x 14 m (46 ft) Egyptian granite, unfluted columns.[x] The capitals are Corinthian. However, if one looks closely there are 2 different types. On the far-left hand side the capitals are more extravagant and the acanthas more pronounced. The granite of these columns is pinkish compared with the other grey ones.

Egyptian rose pink granite shafts of Aswan, with Corinthian capitals on the east side of the portico. This side of the portico had been badly damaged during the Middle Ages. They were restored in the 17th century. The corner column (right in the photo) was brought from Domitian’s villa at Castelgandalfo in 1626, and the other two came from Baths of Nero in 1666. In 1626 Pope Urban VIII Barberini (1568 – 1644, pope: 1623 to 1644) removed the original truss of massive bronze girders which had supported the portico roof and used the 200 tonnes of metal to make eighty cannon for Castel Sant’Angelo. These strong girders suggest that the original roof tiles of the portico were of white marble (the rest of the portico was veneered marble).[xi]

His melting down of the supporting girders prompted the epigram: quod non fecerunt barbari, fecerunt Barberini: where the barbarians failed, the Barberini succeeded.[xii]

Acanthus Plant at the Villa Medici in Rome

The less elaborate capitals of the grey granite columns holding up the portico of the Pantheon. The wonder of modern photography means getting close ups and the remains of an inscription can be seen just above the capitals. It refers to renovations by Septimius Severus and Caracalla in AD 202. No rebuilding occurred though, just refinement.[xiii]

The interior of the portico shows the different granite pillars & their Corinthian capitals. There are also fluted Corinthian pilasters.

The bronze doors are ancient and were in place by the 15th century, but unlikely to be the original as they are too small for the marble doorway.[xiv]

DECORATION: A marble portico & a Rotunda elaborated in stucco  

The portico of the Pantheon is a monumental entrance of Classical tradition. Its pedimented front held up by Corinthian capitals is supported by Egyptian granite shafts with bases and capitals of white Greek (Pentelic) marble. Its exterior was once clad in white marble also.[xv]

However, the rotunda behind the portico is a different matter. Romans were clever at working with the strength of concrete and the ornament of stucco. The rotunda would have been coated in white stucco to look like marble.

A GILT BRONZE DOME – inside and out?

The oculus provides the source of natural light and is open to the elements. The oculus is 8.2m (27ft) in diameter.[xvi] On the inside edge of the oculus is preserved a decorative frieze of sheet bronze. There are five circles of twenty-eight coffers that increase in size outwards from the oculus. It is possible that the interior of the dome was clad in sheet bronze. There is no trace of stuccowork, paint or other decorative finishings, but there is evidence of dowel holes.[xvii]

On the exterior of the dome would have originally been entirely covered with large sheet bronze tiles. However, they were removed by order of the emperor Constans II in AD 663. Now it is protected by sheet lead, some of which may date from the 8th century.[xviii]

Raphael’s Tomb

The interior marble has survived. The tomb of Raphael (1483-1250) lies beneath this niche (known as an aedicula, plural aediculae – a niche covered by a pediment or entablature). In the Pantheon the aediculae have alternate pediments curved and triangle. The columns are alternate unfluted red porphyry or unfluted grey granite or fluted Numidian yellow marble or unfluted grey granite. Other stone cladding decoration includes Phrygian red and white marble. Over the years the stone and paint has undergone many alterations.[xix] However, it still has that strong link back to its original scheme.

Not that the Corinthian column shafts internally are fluted.

When it rains the water runs through and onto the marble floor where there is an almost imperceptible drain.

The Library or Lecture Hall at the Rear?

At the rear of the rotunda is a rectangular hall which maybe the rebuilding of an earlier structure or built around the Trajanic-Hadrianic time of building. It is 46m x 19m (151ft x 62ft). The Via della Palombella cuts through what would have been the original building and the rest of it is buried under the building across from this street. The marble decoration that still exists (can been seen as the ‘white’ bits on the rear in the photo above), demonstrate a possible connection to the Basilica of Neptune. The original Basilica of Neptune had been dedicated by Marcus Agrippa in 25 BC but had been destroyed by the fire of AD 80. It is not a basilica in shape and may have been a lecture hall or library. It is the decoration that links it the Basilica of Neptune – leaping dolphins, acanthus leaves, scallop shells, tridents, and palmettes.[xx]

Egg & Dart, Dentil designs


The Pantheon is a feat of architecture and engineering ingenuity. The 18th-century Grand Tourist would have likely forgotten the arduous and at times dangerous journey to travel to Rome once under its magnificent dome. The complexity of the building and its decoration would require a lifetime of study. It is truly ‘awesome’ and serves as inspiration for the domes on basilicas, cathedrals, Palladian villas, libraries, and garden temples. The Renaissance, then the Baroque, followed by the neo-Classical kept returning to domes. Just think of St. Paul’s Cathedral in London, the Radcliffe Camera in Oxford, Chiswick House, and the U.S. Capitol.



[i] Amanda Claridge, Rome: An Oxford Archaeological Guide, (Oxford: Oxford University Press, 2010), p. 226.

[ii] Claridge, p. 228.

[iii] ’Interior of the Pantheon, Rome by Giovanni Panini, c. 1734’, National Gallery of Art, Wikimedia Commons,     <,_Rome_-_Google_Art_Project.jpg>[accessed: 22 August 2023].

[iv]  asc1, ‘The Pantheon’, Honors Program in Rome, (Washington University, 2004), <,Hadrian%20with%20the%20great%20emperor> [accessed 18 August 2023].

[v] Jonathan Glancey, Eyewitness Companions: Architecture, (London: Dorling Kindersley, 2006) p. 280.

[vi] Glancey, p. 280.

[vii] Glancey, p. 30.

[viii] Nick Gromicko, CMI, & Kenton Shepard, ‘The History of Concrete’, International Association of Certified Home Inspectors, <>  [accessed: 20 August 2023].

[ix] Glancey, p. 111.

[x] Glancey, p. 111.

[xi] Claridge, pp. 228-9.

[xii] Al van Helden, ‘Pope Urban VIII Maffeo Barberini (1568-1644)’, The Galileo Project, Rice University, 1995, <> [accessed: 18 August 2023].

[xiii] Claridge, p. 226.

[xiv] Claridge, p. 229.

[xv] Claridge, p. 226.

[xvi] Gromicko & Shepard, ‘The History of Concrete’.

[xvii] Claridge, p. 230.

[xviii] Claridge, p. 230.

[xix] Claridge, p. 230.

[xx] Claridge, p. 232.


Claridge, Amanda, Rome: An Oxford Archaeological Guide, (Oxford: Oxford University Press, 2010)

Glancey, Jonathan, Eyewitness Companions: Architecture, (London: Dorling Kindersley, 2006)