The Pantheon was originally built by Agrippa during the reign of Augustus, but the monument we see today is largely the restored version from the time of Hadrian. Repairs had been made by Domitian after a fire in 80 CE, yet it was the rebuilding in the early second century that gave the Pantheon its defining feature: the vast concrete dome crowned by the oculus.
The Pantheon is one of the best-preserved ancient buildings in Rome, largely because it was converted into a church in the seventh century. Although it was restored again in the third century by Septimius Severus and Caracalla, whose inscription can still be seen beneath Agrippa’s bronze-lettered dedication, their work does not appear to have significantly altered its overall design.
The current structure was built between 118 and 125 CE. Some scholars believe that Trajan may have begun the rebuilding project and that Hadrian completed it. As Amanda Claridge notes in Rome: An Oxford Archaeological Guide, “Plans for rebuilding were probably put in hand immediately by Trajan and work may have been fairly well advanced by the time he died in 117 CE but not actually finished.”
Lise Hetland, in The Pantheon: From Antiquity to the Present, argues that brick stamps found in the building suggest construction planning may have begun shortly after the fire of 110 CE. The site could have been cleared and materials ordered by around 114 CE. While it is common to call it the “Pantheon of Hadrian,” the evidence suggests a more complex story: Trajan likely initiated the project, and Hadrian brought it to completion.
One possible figure in its design was Apollodorus of Damascus, Trajan’s architect, known for major imperial projects. He lived into Hadrian’s reign but was later executed, possibly after criticizing the emperor’s architectural ideas (as suggested by Cassius Dio, Roman History 69.4). It is conceivable that the innovative rotunda and oculus originated during Trajan’s reign.
In antiquity, the Pantheon did not sit isolated in the open square we see today. Instead, it stood at the southern edge of a large porticoed courtyard and was approached by steps. From the front, the building would have resembled a traditional temple. As Filippo Coarelli explains in Rome and Environs, the massive rotunda behind the porch was almost invisible from the square, creating a dramatic contrast between the conventional exterior and the astonishing interior. Visitors ascending the steps and entering the porch would suddenly encounter the vast domed space – a breathtaking architectural reveal.
The dome remains one of the greatest engineering achievements of the ancient world. It is still the largest unsupported concrete dome ever built. The concrete becomes progressively lighter toward the top, and the thickness of the dome decreases from about 6.4 meters at the base to roughly 1.2 meters near the oculus, which measures 8.5 meters across. The dome spans 44.4 meters in diameter, and a perfect sphere of the same diameter would fit exactly within the building’s height and width. The coffers reduce weight, while hidden arches channel the remaining force into massive supporting piers. The slightly curved floor, with discreet drainage holes, allows rainwater entering through the oculus to flow away.
Despite its brilliance, the Pantheon is not without imperfections. The pediment between the porch and the rotunda appears slightly mismatched. The columns, at 12.2 meters tall, are about three meters shorter than originally intended, creating minor proportional inconsistencies. These flaws, however, do little to diminish the building’s overall harmony.
The Pantheon also differs from a typical Roman temple. It lacks a traditional cella and shows no clear evidence of an exterior altar. Ancient literary references are relatively scarce, appearing mainly in Cassius Dio and the Historia Augusta. Dio (69.7) records that Hadrian sometimes held court in the Pantheon, suggesting it functioned as a public and political space as well as a religious one.
This raises the question: was the Pantheon truly a temple? Paul Roberts, in Ancient Rome in 50 Monuments, suggests that the name may be understood less as “all the gods” and more as “all revered,” possibly referring to the emperor and imperial family. Agrippa’s original Pantheon housed statues of Mars, Venus, Divus Julius, and statues of Agrippa and Augustus in the porch niches. Venus and Mars were deeply connected to the Julian family and Rome’s mythic origins, while Julius Caesar had been deified. Even though Augustus refused divine worship in Rome during his lifetime, the association between religion and imperial authority was clear. The Pantheon may therefore have celebrated both the gods and the imperial household.
The building retains much of its second-century decoration: the colored marble opus sectile floor, many of its columns, and much of the wall veneer. Some elements were lost over time. The Byzantine emperor Constans II removed the bronze roof tiles in the seventh century, and Pope Urban VIII later stripped bronze from the porch ceiling. Bell towers were added in the seventeenth century and removed in the nineteenth.
Today, the Pantheon stands as one of the greatest achievements of Roman architecture. In a city filled with extraordinary monuments, it continues to inspire awe nearly two thousand years after its construction.
Bibliography:
- Claridge, Amanda. Rome: An Oxford Archaeological Guide. Oxford: Oxford University Press, 2010.
- Coarelli, Filippo. Rome and Environs: An Archaeological Guide. Translated by James J. Clauss and Daniel P. Harmon. Berkeley: University of California Press, 2014.
- Hetland, Lise. “Three New Perspectives on the Dating of the Pantheon.” In The Pantheon: From Antiquity to the Present, edited by Tod A. Marder and Mark Wilson Jones, 95–112. Cambridge: Cambridge University Press, 2015.
- Roberts, Paul. Ancient Rome in 50 Monuments. London: Thames & Hudson, 2019.
PANTHEON, a temple which, with the thermae, Stagnum and Euripus, made up the remarkable group of buildings which Agrippa erected in the Campus Martius. According to the inscription on the frieze of the pronaos (CIL vi. 896: M. Agrippa L. f. cos. tertium. Fecit) 1 the temple was built in 27 B.C., but Cassius Dio states that it was finished in 25 B.C.
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It seems probable that the temple was built for the glorification of the gens Iulia, and that it was dedicated in particular to Mars and Venus, the most prominent among the ancestral deities of that family. In the ears of the statue of Venus hung earrings made of the pieces of Cleopatra’s pearls (Plin. NH ix. 121; Macrob. iii. 17. 17). Whether the name refers to the number of deities honoured in the temple (cf. πάνθειον, Rosch. iii. 1555, and the various πάνθεια in Greek lands, DS iv. 315), or means ‘very holy’ (hochheilige, cf. HJ 582; Jord. Symbolae ad historiam religionum Italicarum, KOnigsberg, Index lectionum, 1883), is uncertain: but Mommsen’s conjecture that the seven niches were occupied by the seven planetary deities is attractive, and Hilsen is now in favour of it. There is no probability in Cassius Dio’s second explanation (v. supra).
In the pronaos of Agrippa’s building were statues of himself and Augustus (Cass. Dio loc. cit.), and on the gable were sculptured ornaments of note (Plin. NH xxxvi. 38). The decoration was done by Diogenes of Athens, and Pliny goes on to say (loc. cit.) in columnis templi eius Caryatides probantur inter paucaoperum (cf. xxxiv. 13: Syracusana (i.e. aenea) sunt in Pantheo capitacolumnarum a M. Agrippa posita). The position of these Caryatides has been much discussed, but is quite uncertain (Alt. 62-63).
The Pantheon of Agrippa was burned in 80 A.D. (Cass. Dio Ixvi. 24. 2) and restored by Domitian (Chron. 146; Hier. a. Abr. 2105; cf. perhaps 2101). Again, in the reign of Trajan, it was struck by lightning and burned (Oros. vii. 12; Hier. a. Abr. 2127). The restoration by Hadrian (Hist. Aug. Hadr. 19) carried out after 126 (AJA 1912, 421) was in fact an entirely new construction, for even the foundations of the existing building date from that time. The inscription (see above) was probably placed by Hadrian in accordance with his well-known principle in such cases. The restoration ascribed to Antoninus Pius (Hist. Aug. Pius 8:instauratum … templum Agrippae) may refer only to the completion of Hadrian’s building. Finally, a restoration by Severus and Caracalla in 202 A.D. is recorded in the lower inscription on the architrave (CIL vi. 896).2 In January, 59 A.D., the Arval Brethren met in the Pantheon (CIL vi. 2041); Hadrian held court in his restored edifice (Cass. Dio lxix. 7. I); Ammianus (xvi. 10. 14: Pantheum velut regionem teretem speciosa celsitudine fornicatam) speaks of it as one of the wonders of Rome; and it is mentioned in Reg. (Not. Reg. IX).
The building faces due north; it consists of a huge rotunda preceded by a pronaos. The former is a drum of brick-faced concrete, in which numerous brickstamps of the time of Hadrian 3（CIL xv. 276, 362, 649 a, 811 b, c, I 106 b, 1406) have been found.4 which is 6.20 metres thick; the structure of it is most complex and well thought out. On the ground level the amount of solid wall is lessened by seven large niches, alternately trapezoidal and curved (the place of one of the latter being taken by the entrance, which faces due north), and by eight void spaces in the masses of masonry between them, while in the upper story there are chambers above the niches, also reached by an external gallery supported by the middle of the three cornices which ran round the dome. In front of these masses are rectangular projections decorated with columns and pediments alternately triangular and curved, which have been converted into altars. The pavement is composed of slabs of granite, porphyry and coloured marbles; and so is the facing of the walls of the drum, which is, however, only preserved as far as the entablature supported by the columns and pilasters, the facing of the attic having been removed in 1747 (for drawings, cf. NS 1881, 264, 292; HJ 585, n. 75).5 The ceiling of the dome is coffered, and was originally gilded ; in the top of it is a circular opening surrounded by a cornice in bronze, 9 metres in diameter, through which light is admitted. The height from it to the pavement is 43.20 metres (144 feet), the same as the inner diameter of the drum. The walls are built of brick-faced concrete, with a complicated system of relieving arches, corresponding to the chambers in the drum, which extend as far as the second row of coffers of the dome; the method of construction of the upper portion is somewhat uncertain (the existence of ribs cannot be proved), but is probably of horizontal courses of bricks gradually inclined inwards. Pumice stone is used in the core for the sake of increased lightness.
The ancient bronze doors are still preserved, though they were repaired in the sixteenth century. The pronaos is rectangular, 34 metres wide and 13.60 deep, and has three rows of Corinthian columns, eight of grey granite in the front row and four of red granite in each of the second and third. Of those which were missing at the east end (which cannot possibly have been removed in 1545 (DAP 2. xv. 373, 374), as they were already absent earlier (compare Heemskerck i. 10; ii. 21; Giovannoli, Roma Antica (1615), ii. 11), the corner column was replaced by Urban VIII with a column of red granite, and the other two by Alexander VII, with grey columns from the thermae Alexandrinae.6 The columns support a triangular pediment, in the field of which were bronze decorations; in the frieze is the inscription of Agrippa; and the roof of the portico behind was supported by bronze trusses. This portico was not built after the rotunda, as recent investigations by Colini and Gismondi have shown (BC 1926, 67-92), and the capitals of its columns are exactly like those of the interior (RA 122), though the entasis of the columns differs (Mem. Am. Acad. iv. 122, 142). In front of it was an open space surrounded by colonnades. The hall at the back belongs also to Hadrian’s time, and so do the constructions on the east in their first form. The exterior of the drum was therefore hardly seen in ancient times.
The podium of the earlier structure, built by Agrippa, lies about 2.50 metres below the pavement of the later portico; it was rectangular, 43.76 metres wide and 19.82 deep, and faced south, so that the front line of columns of the latter rests on its back wall, while the position of the doorways of the two buildings almost coincides. To the south of the earlier building was a pronaos 21.26 metres wide, so that the plan was similar to that of the temple of Concord.7 At 2.15 metres below the pavement of the rotunda there was an earlier marble pavement, which probably belonged to an open area in front of the earlier structure; 8 but a marble pavement of an intermediate period (perhaps that of Domitian) was also found actually above this earlier structure, but below the marble pavement of the pronaos.
The restoration of Severus and Caracalla has been already mentioned; but after it, except for the account by Ammianus Marcellinus, already cited, of Constantius’ visit to it, we hear nothing 9 of its history until in 609 Boniface IV dedicated the building as the church of S. Maria ad Martyres (LP lxviii. 2). Constantius II removed the bronze tiles in 663 (ib. lxxviii. 3; cf. Paul Diac. Hist. Langob. 5. II; AJA 1899, 40); and it was only Gregory III who placed a lead roof over it (ib. xcii. 12). That the pine-cone of the Vatican came from the Pantheon is a mediaeval fable; it was a fountain perhaps connected with the SERAPEUM(q.v.).
The description of it by Magister Gregorius in the twelfth century (JRS 1919, 36-37, 53) is interesting, especially for the mention of the sarcophagi, baths and figures which stood in front of the portico (cf. DuP 131 for further information as to its history in the Renaissance, during which it was a continual subject of study for artists and architects). A porphyry urn (from the thermae of Agrippa), added by Leo X, now serves as the sarcophagus of Clement XII in the Lateran. For its mediaeval decoration, see BCr 1912, 25.
Martin V repaired the lead roof (LPD ii. 544) and Nicholas V did the same. Raphael is among the most illustrious of the worthies of the Renaissance who are buried here.
The removal of the roof trusses of the portico by Urban VIII gave rise to the famous pasquinade ‘quod non fecerunt barbari fecerunt Barberini‘ (PBS ii. 38, No. 65 a; vi. 202-204).
1 The bronze letters are modern: see CIL vi. p. 3073, No. 31196.
2 What it amounted to is quite uncertain, for no traces of their work can be recognised with any certainty (JRS 1925, 125).
3 ‘For others, which confirm the date, cf. Mitt. 1893, 313, 314.
4 The name of Sabina, his wife, is said to have been read on the marble of the main apse (not on the pavonazzetto columns); see HJ 585, n. 74.
5 Add a drawing in Cod. Escurial. f. 30, and another by Raphael (Uffizi 164; Bartoli, i. lxiv. 99).
6 The corner column only lacked the capital, and why it was removed by Urban VIII is not clear. The capital bears his badge (the Barberini bee) just as the other two capitals bear the Chigi star of Alexander VII. See Roma v. (1927) 471.
7 In this case there would be no room for the decastyle portico which some suppose (cf. SScR 71-73, who conjectures that it is represented in the well-known relief of a decastyle temple (HF 1146, 1412; cf. PBS iv. 247; see VENUS ET ROMA, TEMPLUM)). Chedanne, however, whose results are not yet published, thought that the entablature of the pronaos had originally belonged to a decastyle temple, which he supposed to have been peripteral (HJ 589).
8 The wall of opus reticulatum which was found to be concentric with the drum of the rotunda may have been an enclosure wall, or may have served as part of the foundations of the drum; but the former is more likely, as it was about 2 feet high, with a rounded top like a garden wall. Whether the slope of the earlier pavement from the centre towards the circumference was due to design or to the weight of the later rotunda, is doubtful.
9 There is a mention of it in Cod. Theod. xiiii. 3. 10, lecta in Pantheo non. Nov. (368 or 370 A.D.). Cf. BC 1926, 64, 65.
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Cite this page as: Darius Arya, The American Institute for Roman Culture, “Pantheon,” Ancient Rome Live. Last modified 2/22/2026. https://ancientromelive.org/pantheon/
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