34233 Fuldatal GERMANY
In order to hear clearly the acoustic phenomena in the Rotunda of the Roman Pantheon, it is necessary is to close all openings and activate a single sound source. On 21 March 2002, meeting participants were allowed to carry out small acoustic experiments after the rotunda closed to the public, from 7:30 pm until 7:55 pm (at which time the automatic security alarm is activated); at the same time together it was possible to observe the optical effects of reflected moonlight. I undertook a simple but effective acoustic experiment. I positioned myself at the centre of the Rotunda over the bronze ring in the floor, bent my head directly back so that the sound waves were directed at the dome and produced three notes in harmony, one after another: C-E-G (do-mi-fa). The volume of the resulting sound was amazing, because it did not sound as though it were coming from a single untrained voice, but rather from a powerful opera singer. After the original notes faded an echo-like reverberation could be heard which had a completely different dimension of sound. The three notes were apparently reflected back to the listener from the surface of the dome. The notes were perceived, not one after the other, but as a harmonic chord, with the sounds layered on top of each other, as if some one had played a three-note chord on an instrument. In other words, they were heard in unison. By means of the architecture, the rotunda created a polyphonal chord out of three individual notes. The difference between a musical instrument and the architecture is important: where in an instrument the single keys or strings each produce a note, and simultaneous strokes produce chords, in the rotunda a chord was created even though the individual notes were not sounded simultaneously. This can only be possible through the focussing and reflecting influence of the coffers. This phenomenon supports the hypothesis that the musical polyphony of Western European culture is based on the "harmonising" effect its architecture. Greek antiquity, Arabian, and Far Eastern music are all lacking polyphony.
It is easy to arrive at the conclusion that the effect of polyphony is achieved through the arrangement of the coffers, which, thanks to steep, short, graduations on their upper halves together with slanting smaller graduation on the lower, are directly aimed at the spectator. Proof of this must still be verified using tape-recorder and oscillograph. The exact reverberation of sound in the Pantheon must be analysed to determine the acoustic consequences of the architectural design of the Rotunda and the dome.
But the phenomenon proves that the musical component of the ancient quadrivium based on arithmetic, music, geometry, and astronomy is capable of generating not only a numerical proportional architectural system but also a genuine musical effect: the Rotunda is capable of producing a genuine polyphony.
It should also not be forgotten that the rays of the sun passing through the oculus of the Rotunda move along the meridian line over the course of the year (Fig. 1). Although this is not audible, it creates calculable harmonic mathematical intervals. During the summer, the sun's rays shine at noon on the floor; during the spring and autumn, they shine on the string courses above the inner row of columns and the attic; during the winter, they shine on the coffers of the dome. The rays act as the bridge of a monochord whose strings are represented by the string courses arranged in parallel rows. The positions of the sunbeams in the Pantheon precisely reproduce the intervals of proportion of the fifth, the fourth, the whole note and the octave. With regards to the position of the bridge of the monochord, the notes get higher as the bridge is moved so that its position shortens the string length, but the interval remains the same. This was demonstrated by the helikon, an ancient instrument similar to a guitar used to teach music theory. The notes get higher, but the intervals remain the same. The same phenomena is produced by the sunbeams as they strike the different levels of the Rotunda. The imaginary lines extended to the north are always dissected at the same interval, whether the angle of the sunbeam is high (summer) or low (winter).
A useful indication of one scientific use of the Pantheon is the citation in the Oxyrhynchus Papyrus 412 (now in the Dept of Manuscripts, The British Museum) by Sextus Julius Africanus, a Christian who built a library in the Pantheon for Alexander Severus about 230-40 AD. He refers to a translation of the Odyssey that he wrote himself, saying that up to the thirteen verse was to be found, among other things, "in Rome by the thermal baths of Alexander in the beautiful library of the Pantheon, which I built myself for Caesar (as his appointed architect)."  Since Julius Africanus had spent a long period in Alexandria studying and writing papers on natural sciences, it can be hypothesized that the Pantheon library was in the Alexandrian style.
It should also be noted that the cult of the Arval Brethren was practiced in the Pantheon at that time. This involved the calculation of times for the planting and harvesting of crops, acts which at that time, as today, could be related to the religious calendar, indicating that astronomical questions were also considered. The mysterious but verifiable fact that the line from of the edge of the dome through the middle of the oculus produces an angle which is exactly the latitude of Rome (41.8°) and the angle of the ecliptic at that time (23.41°) touches on and accentuates all of the architectural elements from the pronaos and the Rotunda both internally and externally (Fig. 2).. This supports the hypothesis that the library, situated in this southern sector, would have had a room for the observation of the sky. However, in order to view the circumpolar sky in the oculus an opening would have been required at the southern edge of the dome. Our investigation during the course of our meeting revealed a bricked-up rectangular slit roughly forty centimetres wide and three meters high, placed exactly on the southern part of the dome, not at all related to the other tension ring cracks filled in after the construction of the dome (Fig. 3).
These cracks are irregular and narrower in shape, and recorded as being in situ by Alberto Terenzio in 1930. They were also verified using a computer simulation by R. Mark and P. Hutchinson in 1986. It can also be noted that the inner coffers (on the opposite side as well) are noticeably irregular and the material appears not to be as consistent as the others, which is another indication of a later closing of this particular opening.
This slit that we noted could really have been an observation void in the wall of the dome, allowing the position of stars to be fixed using a diaopter mounted on glass plates or also to determine more accurately the movement of the position of the beginning of spring along the ecliptic (precession). The precession led to the rise and fall of the zodiac signs in the so-called Platonic Year (roughly 26.000 years). A reassessment of this hypothesis is subject to obtaining permission to drill a hole for a photoscope or even completely open the slit itself.
EDITOR'S NOTE: First published in German with an English translation in the Werkbund Nord, 2002-2, and republished in the Nexus Network Journal by permission. Revised English translation by Kim Williams. Original title: "Frühe Mehrstimmigkeit. Das Pantheon ein Klangkörper".
 Quoted in W. Wischmeyer, Von Golgatha bis Ponte Molle, Göttingen, 1992, p. 45. return to text
 Cf. Gert Sperling, Das Pantheon in Rom: Abbild und Mass des Kosmos, pic. 113, p. 203. return to text
 R. Mark and P. Hutchinson, "On the Structure of the Roman Pantheon", Art Bulletin 68, March 1986, p. 22-34. return to text
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