The Zodiacal "curved disc" of Chevroches (France)

A disc

The Gallo-Roman site of Chevroches is located at the north west province of Burgundy in the Nièvre department. During the roman period, the site was included in the Eduens territory. Their former celtic capital, Bibracte (Mont Beuvray) was changed into Augustodunum (Autun).
The Future implantation of a vacation community, programmed between a limestone spur and the alluvial plain of the Yonne, required the realisation of a preventive archaeological excavation between 2001 and 2002 by INRAP.
An unseen small gallo-roman town which is expanded on 4 hectares has been discoverded.
The site was very rich as the Roman occupation lasted from the second quarter of the 1St century until the 5th century AD.
Metal-working was an important activity during the 4Th century (iron and bronze) and was organised in large workshops installed in small zones delimited by streets.
Many noteworthy elements of furniture made of bronze, iron or lead have been discovered: tools, domestic elements, harnesses, bars and scrap from the forge, elements of finery and even a decorative element of an openwork sheath.
The archaeological site of Chevroches counts among the more important results of preventive excavations in the region. A rich collection of objects coming from metallic deposits was renovated, with a financial help from the Archeological Museum of Dijon.
And then, the renovators of the laboratory of metal archaeology of Jarville-Nancy, discovered firstly classified as a decorative phalerae (of a harness ?), was in fact one of theses particularly rare "savant object"...

The dimensions of the curved disc are:
Diam. : 6,45 cm
H.: 1,30 cm
Thickness: 0,5 mm
This curved disc is divided in 12 equal quarters, and in each quarter, you can read 3 layered words, all engraved in Greek letters :
The external line corresponds to the 12 Egyptians months;
The median line to the 12 zodiacal signs at dative
The inside line, to the 12 roman months.

Stages of manufacturing :
1. An artisan first manufactured the form of the curved disc by hammering out a bronze slab (around 100 mm diameter), giving it its rounded aspect.

2. An experimented engraver then chiseled 3 approximate concentric circles. The one on the circumference is the less preserved. It is deleted on 2 places (usury?).
A circular hole of 5 mm was pierced on the top of the object. It is lightly decentred from the other circles putting into perspective the accuracy of this « scientific object ».
3. The engraver divided the surface between the second circle and the periphery of the curved disc in 3 equal parts of 30° each. Then, he defined the perimeter of the instrument by subdividing each of the 12 parts delimited previously by 6 equal graduations in principle.
4. The inscriptions have been engraved during a last step. Indeed the engraving of some letters are above some lines or some circles previously engraved.
5. Then this curved disc have probably been fixed on a (spherical?) support, by the way of a tin brazing visible on the inferior face of the object. The instrument may have been maintained in a diametric way on a part of its diameter. A deformation on its lateral part tends to show that this object may have been extracted of its support when somebody thrown it out.

We can start the reading of this curved disc by Thoth, the first Egyptian month, which begins on our 28th day of august (or 29 for leap year).
This object doesn’t consider the 5 added days (6 for leap years since Julian calendar’s reform).
Indeed the civil Egyptian calendar counted regular months of 30 days, which had the consequence of 5 to 6 days addition at the end of each year.
Here, the concurrence between Roman and Egyptian months is obtained in such approximate way...
The use of Greek alphabet, the references at Egyptian's zodiacal signs and months, the attempt to make a correspondence between Egyptian and Roman calendar...
This rare object may have been used by someone with solid astrologic knowledge. If the practice came from a long tradition, it’s procedures are really complex to analyse.
The technique of embossing some metal is a speciality in Gaule.
This object is certainly inspired of an Egyptian model, created around the Alexandrian School, because of the ability to use Greek language and its abbreviations.
The stratigraphic context : 340 / 350 AD.
The Epigraphic estimation (P. Cauderlier) : End of 3th century AD / 4th century AD.

1st Hypothesis:

An astro(LO)gic use
The astrologist began with overlaying his sky map (drawn on papyrus or on wood table for example) with the ecliptic’s median plan (oriented on the top of the sky), and then he installed 2 zodiacal signs.
Then with the help of calculation tables (like « Theon’s tables » known in antiquity’s literature), he determined the middle and the bottom of the sky, and then he established the position of the planets by looking his sky map. By turning the table on 180°, he wrote the name of the zodiac signs. With an instrument like Chevroche’s curved disc, the astrologist could transfer his day data to establish his customer’s horoscope or to look the positive and negative dates ( like Tryphon’s Horoscope – University of Oxford, England).
But the practise of this discipline is complex and requires the assimilation of specific notions, which would be long to develop here.
This astrologic (?) curved disc is really extraordinary; it seems the unique object of this type in the antic world. However, other testimonies of astrologic practices during the roman period are attested.
Among these ones it is useful to record an archaeological discover as rare as this one: on the site of Grand (Vosges’ department, France) at the end of the sixties.Two folding diptychs in ivory showing a sky map organised in zodiacs where the figures are emphasized in the dimple, by red, black and gold.

2nd Hypothesis: an astronomical use and a element of more complex mechanism

The traces of a tin brazing on the curved disc let us however think about a more complex mechanism.
Another cousin of the Chevroches’ curved disc, the Alesia’s diary.
This object is a thin circular bronze slab of 11cm of diameter discovered during a 20 st century’s excavation in Alise Sainte Reine (Burgundy). I was “lost” in a private museum collection …
We can also notice this astronomic object, recently re- discovered. Indeed, C. Vernou (musée archéologique de Dijon, UMR 5594), by checking all the objects founded in the region since XIXth century; find the drawing of this curious object.

It is a disc cut into 14 nicks, pierced in the centre, and where the name of the 7 planets is engraved face to face.
The planets are signalled by the 3 first letters of the deities corresponding with the 7 week’s days.

3rd Hypothesis:

Element of armillary sphere, globes, anaphoric clocks ? But the clues are too small for the moment.

The scientific research group "Instruments et mécanismes antiques en Gaule Romaine" has been created to collect and study recent finds (archeological excavations) and old finds, "lost" in museums and private collections, and understand there use (Horoscopes, astronomic calculations, calendars, etc).

The Team consists of:
Frédéric Devevey (Inrap/UMR 6249-CNRS)
Aurélie Rousseau (Archaeologist)
Christian Vernou (Musée arch. de Dijon / UMR 5594)
Patrice Cauderlier (Université de Bourgogne / Ecole Normale Supérieure de Paris)
Pierre Causeret (Observatoire astronomique de Bourgogne)
Claudine Magister - Vernou (Archaeologist and designer)

> Read more about the "Chevroches disc" at the wesites of the Revue Archéologique de l'Est and INRAP.