Address: piazza della Rotonda (pedestrian area)

The monument that we know is the result of a long history, of which the first happenings concerning it are rather obscure. According to Cesare D'Onofrio, one of the major romanists still living, the Pantheon would have been built on the place where, according to the narrations of the archaic sources Romulus 'ascended' to heaven during a ceremony, in Campo Marzo, interrupted by an unforeseen and violent storm.

For centuries in this place, in the day of the disappearance of Romulus, rites and processions took place which brought to mind this supernatural event.
May be already existed a sanctuary, even if small, dedicated to those practises. And when, in the year 27 b.c. Marcus Vespasianus Agrippa erected the Pantheon, he did not choose at random the traditional theatre of the apotheosis of the founder of Rome : Agrippa was the son-in-law and the prince architect of Augustus who wanted to appear as the new Romulus, the new founder of the universal fortune of the City. The temple was dedicated to the seven planetary divinities. It is very late, medieval, the fanciful legend of the simulacra of all the provinces of the empire collected indoor which, by magic, pointed out the centres of rebellions or the external threats. Many, in different times, are the conjectures about the complessive style and the dimensions of the edifice of Agrippa : certainly, it was rotondo, as to-day, and as the popular memory has roots as deep as it is inextirpable, probably it traces back to the origine the name la Rotonda, with which the Romans have always hinted at the monument : still to-day, it is this the name of the square in front of it.
No matter as it could be, the first Pantheon met with fire and other calamities, it was twice restored till Adrian, the great architect emperor, may be completely remade it. Here also the facts are insecure, quasi certainly it is due to Adrian the nice pronaos, with sixteen high columns, while the dimentions of the true and proper 'rotonda' were amplified up to support the beautiful cupola in concrete, a vanguard technique, probably ealized filling up with soil the underlying emptiness.

When the reconstruction ended, Adrian modestly wanted to bring back to memory the first architect and he restored, on the pediment, the commemorative inscription of Agrippa : M. AGRIPPA L F COSTERTIUM FECIT 'Marcus Agrippa, son of Lucius, Consul for the third time, built', in bronze, as

today it is seen: the actual one is however a copy of the end of the 8th century, in place of the ancient incription which was despoiled, in one of the so many incursions.
The Pantheon of Adrian's wall thickness is of six metres and twenty centimetres, and the interior has harmoniously distanced niches, alternatively rectangular and semicircular, the inside walls are still, in greater part, decorated with marbles which originated from the quarries of the empire. The diametre and the height of the interior are equal : their measures are fourty three metres and thirty centimetres, equal to 150 roman feet : it means that, in this space a sphere of this diametre could be installed. Already, this calculation allows to suppose that the time expressed a cosmic symbolism ; and the hypothesis is reinforced by the fact that the axis of the edifice has a small difference as regards the north-south direction, evidently willed because the difference allows the observation of an astrological-calendar phenomenon : at 12, on the 21 of June, the summer solstice, the ray of the sun which crosses the great 'eye' of the cupola, falls at the centre of the entrance portal ; with the months going forward, the ray rises, but always in the same direction. In summary the Pantheon was a 'solar' temple, and as such, showed itself to the visitors, immediately invested by heat and the light of the planet. It is probable that the 'eye', so great, nearly nine metres in diametre, served also for nocturnal astronomical observations.
It was transformed into a church under Pope Boniface IV who, in 609 d.c. dedicated it to the Madonna and to all the martyrs. Rightly, on account of this new utilization, the imponent monument succeeded to preserve inalterated its essential lines and to reach us practically integral. Masterpiece of skill and technic of the roman architecture, the Pantheon possesses the largest cupola that has been built : in fact it has a diametre of nearly 43 metres.
Although the real and true cupola begins from the second big cornice, at first sight, one could believe that all the structure of the underlying cella had been made as a tambour for the splendid roofing. An ancient legend narrates that during its construction, the tambour had been completely covered with soil which, afterwards, would have made the Montecitorio Hill. Outwardly, the top is covered with lead, but originally it was richly covered with golden bronze tiles. It was stripped of its precious material by Costantia II in 633, and we can only now imagine it nice and scintillating in the hot roman light.

If its exterior is decidedly sober, of quite other consistence is its interior aspect. We can in fact admire series of twenty eight caissons superimposed in five orders which gradually tighten up to attain, on the summit a diametre of only nine metres. And, with parallele effect, the consistence of the used materials diminishes and these materials become progressively always lighter. And exactly in the higher part is found the opened ring, the so said 'eye'. To the 'eye' also is linked a medieval legend according to which, it was considered as the ancient seat of the big bronze pine which actually is found in the homonymous courtyard, in Vatican.
The Pantheon is the roman monument which boasts of the major number of supremacies. It has the largest cupola of all the history of the architecture ; it is the best preserved among the ancient edifices of the City ; it is the only one -among these- to have maintain, up to nowadays, in two millennia, the same religious function for which it was constructed ; it is the architectonic work of antiquity the most copied and imitated, not only in Italy ; by its shape, were inspired Andrea Palladeo, the Georgian architects, the neo-classics and their many followers up to a main part of the 8th century. Loaded with so many glories, the Pantheon towers, with serenity, in front of the precious fountain, with the egyptian obelisk, from its harmonious lines, issues a sense of unshakable stability.
Certainly, the edifice, as we see it to-day, even so nice, is as if it were stripped. The most brilliant decorations which enriched it, in origine, have infact disappeared : are missing, among other things, the bronze golden tiles which entirely covered the cupola, and the great bronzy relief which surely (the holes for the gromps remain) decorated the tympanum. To imagine it, as it was before, is an alluring game for the visual fantasy. But even 'stripped' the Pantheon looses little of its extraordinery grandeur. The excessive floying of the walls in bricks, out of the cylinder, allows to admire the expertness of the engineers as builders, with these powerful discharge arches which sustain the weight of the massive structure.
In 1892 the French architect George Chedanne discovered, at a depth of about two and a half metres, under the floor of the pronaos, a platform made of thick travertine slabs and slabs moulded with marble on the sides for a total of 43.76 x 19.82, measures superior to those of the actual porch which measures 32.20x 13.50. Under the forepart, at the same level there was a pit, narrower of 21.26 x 10.20 m. and further than this one, on the same axis, there was a circular area limited by a reticulated wall and paved with marble slabs. There was, at the end, at an intermediate level of m. 1.85, under the pronaos, an area paved always with marble, with a slight slope towards the west. Probably, the great rotunda constitued the cell of the Pantheon of Agrippa with wooden covering roof and the pit smaller then the pronaos. The second marble floor, under the pronaos, was attributed to an intermedium restauration of Domiziano.
For what concerns the simultaneity of the three structures, rotunda (circular building), the fore-part and pronaos, the excavating executed by Colini and Gismondi shows the different methods in the construction ot the different parts. The rotunda in fact lies on a continuous foundation in ring in opus coementicium, wide m. 7.20, the fore-part on a foundation with an identical pit, but posterior to the circular one, as it leans following the holes of the niches and of the door. The porch, to end, does not have an homogeneous foundation for what concerns the travertine blocks on which rest the front columns, and the concrete walls parallel to the axis of the temple on which lie the other files of columns. From that diversity of methods two opinions once originated : one according to which the porch is seen to be posterior to the fore-part, according to Beltrame, an the other, sustained by Colini and Gismondi who affirm that the porch and the fore-part are of the same period, and that the differences are exclusively due to building reasons.