A pair of stone disks found in the Northeastern part of Italy may be representations of the sky, and one disk with chisel marks may be the oldest star map ever discovered. The two stones were found at bronze age hillside fortifications that were occupied between 1800 and 1650 BCE, to the late Iron Age approximately 400 BCE. One stone was located on Gradina on the Brijun/Brioni Maggiore Island facing the southern coast of Istria, Croatia. The second one is from Rupinpiccolo/Repnic,ˇ located in the Trieste Karst.

The first stone disk does not contain any markings and archaeologists believe it may be a representation of the sun. The second stone shows chisel marks that are believed to represent portions of various constellations, known as asterisms, according to the study by archaeologist Paolo Molaro from the Ca' Foscari University of Venice and Frederico Bernardini an astronomer with Italy’s National Institute of Astrophysics.

“There is a total of 24 chisel marks on the front face of the stone disk and 5 on the back,” the study, published in Astronomische Nachrichten, says. The 5 chisel marks on the back of the disk show a strong correlation with the constellation Cassiopia while the 24 chisel marks on the front are divided into three separate groupings. The study authors believe these marks represent the tail of Scorpius and portions of Orion and the Pleiades.

“The deepest mark with depth of 22 mm corresponds to Antares, the brightest star of the Scorpius constellation,” the study says.

To support this, the researchers plotted the chisel marks from the stone and overlayed them onto depictions of the constellations using Stellarium. They conducted statistical analysis on the Right Ascension and Declination positions of the marks as compared to the stars on a digitized sky survey and, after adjusting for differences in scale, typically found a high level of correlation using the Pearson correlation coefficient.

The tail of Scorpius seems to correlate best with values of 0.988 for declination and 0.995 for right ascension. The Pearson correlation coefficient is a measure of correlation based on observed data. It limits errors - due to things like impreciseness in the chisel marks - as it does not consider the uncertainty of the data.

Despite that uncertainty, the high level of correlation for most of the marks, reported as r=0.994, has led the study authors to conclude that the marks were not produced accidentally and were, in fact, quite intentional. However, the stone does contain some problems, of the 24 chisel marks on the front face, one mark does not seem to correlate well with any celestial object. And the Orion portion of the constellation is missing two stars which seems odd. The authors propose that these stars may have been obscured by being eroded away over time.

They conclude their study acknowledging that, due to the uncertainty and these few problems more research is needed.

“We regard this interpretation as a suggestion and we urge additional studies and searches of other astronomical evidence in the civilization of the Castellieri to avoid fanciful interpretations.”

A news article on the discovery can be found on the INAF’s website: https://www.media.inaf.it/2023/12/22/mappa-celeste-rupinpiccolo/ A PDF of the study can be found here: