Archaeological discoveries

From the Neo-Babylonian tablets to the Nebra disc, the astronomers of prehistory

From Mesopotamia to the Vallée des Merveilles in Provence, via the Nebra disc, intriguing representations testify to the same attention to certain celestial figures, millennia ago.

A replica of the Nebra disk, in 2019.

NEBRA DISC. This article by Azar Khalatbari is taken from the special issue of Sciences et avenir from July-August 2011. It is about the disk of Nebra, a piece considered to be the first human representation of the celestial vault, but whose new estimate of the age comes to question this characteristic:it would indeed be a thousand years younger than we thought.

"It's like the murmur of the Mediterranean reaching us across the millennia", marvels Henry de Lumley. Director of the Institute of Human Paleontology of the Albert I Foundation, this prehistorian spent two decades questioning, with his collaborators, the meaning of recurring representations engraved here and there by ancient civilizations around the Mediterranean. Today, at the end of a work bringing together prehistorians and astronomers, he can formulate an attractive hypothesis:across borders and ages, all these peoples shared the same knowledge of the constellations and watched for the appearance of the same stars – in l this case, the few stars visible to the naked eye in the Pleiades cluster, in the constellation of Taurus – to follow the seasons and organize their daily tasks:ploughing, sowing, harvesting.

To decipher the enigma, you have to anchor yourself in the historical and mythological context of ancient civilizations

At the origin of this investigation, an intriguing figure:six or seven cupules close together, like a bunch of grapes. It appears on neo-Babylonian or Mesopotamian tablets dated from 2000 to 1500 before our era, on neo-Assyrian stelae from - 800, on the rock of the Hemma plateau (Syria) in the year one thousand before our era, on the metal disc found in Nebra in Germany, which is thought to have originated in the Alps; or on the clay one found at Phaestos (Crete), and dating like him from -1600. We find, above all, this figure among the thousands of drawings engraved between - 3800 and - 1800 on the slopes of Mount Bégo, in the Vallée des Merveilles, a site in the hinterland of Nice that Henry de Lumley has been studying for years.

Why this ubiquity?"Of course, we can only speculate, says Annie Echassoux, from the departmental laboratory of prehistory at Lazaret, in Nice.But one thing is certain:the engravings from this period are not arranged haphazardly. For example, the 40,000 signs of Mount Bego are only linked in 150 ways. These are probably messages that are not supported by a write". The cluster is, thus, sometimes represented associated with a halberd, often next to a crescent moon and a solar disk, other times near a cultivated field...

To decipher the enigma, we must anchor ourselves in the historical and mythological context of ancient civilizations. The investigation therefore continued in the first texts available for the region, those of the ancient period. "A whole literature has come down to us around the Pleiades from around the Mediterranean, says Henry de Lumley, describing them in clusters of six points. And in these texts, they are linked to the cycle of the seasons" . The oldest quotes date back to the 8th century BC:Homer in the Illiad refers to it, and Hesiod in Works and Days , advises:"When the Pleiades, daughters of Atlas, rise, begin the harvest, and set to work when they set..."

Five centuries later, Aratos de Soles, poet and astronomer, mentions them in his Phenomena:"They are small and not very bright, but they pass in the morning and evening, when, by order of Zeus, they show the summer and the beginning of winter and the approach of plowing..." Cicero, two centuries later, in Carmina Aratea:"They announce to mortals that they must entrust their seeds to the Earth". Hygin, Virgil, Germanicus also refer to it. Pliny the Elder, in the first century of our era, underlined in his Natural History:"It is the moment when the vine and the olive tree conceive, because the Pleiades are their star" . It remained to be demonstrated how the Pleiades could announce the beginning of spring or the date of sowing, whereas today they are no longer associated with these times of the year.

Above the same point on Earth, the sky at the time did not present the same constellations as today

It was again at Mont Bégo that the researchers went to find the answer. The Pleiades are engraved there on two rocks 140 meters apart, where there are halberds whose handles are oriented east-west. On one, the cluster is shown to the west above the blade, while on the other, it appears to the southwest to the left of the handle. If we consider the east-west axis as a horizon, the stars are below and above "as if to represent a heliacal rising and setting (1) of the Pleiades" , says Henry de Lumley. Two very specific periods of the year.

To determine their importance, it was necessary to reconstruct the sky of the time. Because if today the axis of rotation of our planet points towards the Polar Star, 3000 years before our era, it indicated the alpha star of the Dragon. Result:above the same point on Earth, the sky of the time did not present the same constellations as today. Thanks to the dating of the engravings and the calculation of the ephemeris, Patrick Rocher, of the Institute of Celestial Mechanics of the Paris Observatory, deduced the direction towards which the axis of the pole was then pointing and, consequently, the dates of the year corresponding to the heliacal rising and setting of the Pleiades. His calculations indicate that the vernal equinox coincided with sunrise around -4500, sunset around -1300.

"These dates include precisely the time when the site was frequented, that is to say between 3300 and 2300 before our era" , he points out. This means that during this period, the heliacal rising or setting of the Pleiades was close to the vernal equinox. Likewise, during the millennium before our era, the setting of the Pleiades was still close to the vernal equinox – hence the references of Pliny and Cicero. Because in a thousand years, the constellations shift only 13 degrees in the sky (2). Based on these clues, Henry de Lumley imagines a sacred rite:"It is possible that once a year, a small group, perhaps led by a priest, climbed Mount Bégo to watch for the beginning of the beautiful days" . Work in the fields could then begin.

1. Rising or setting heliacal:is said of the rising of a star when, once a year, it appears on the horizon just before sunrise or disappears just after sunset. 2. The axis of rotation of the Earth points in the same direction every 25,800 years:this is the precession of the equinoxes.