The Rosetta Stone and the Nemrud Nomos: the discovery of significant textual and astronomical similarities

The Nomos of Commagene is proclaimed by king Antiochus I (Dörner and Young, 1996; Crijns, 2014). The text is inscribed at the back of five colossal statues on top of Mt. Nemrud, the paramount sanctuary (Fig. 1). The Rosetta text is proclaimed by the Egyptian priests, who glorify the benevolent Ptolemaic king and his divine cult. The Ptolemies issued a series of decrees to cement their rule over the course of their reign (Manning, 2012). The Rosetta Stone of Ptolemy V is the most famous one, because it enabled the deciphering of hieroglyphs (Wallis Budge, 1913). The decree was issued in 196 BCE on behalf of king Ptolemy V to commemorate his coronation nine years before, in 205 BCE. In that year, his father Ptolemy IV assigned his five year old son as co-ruler. The coronation of the boy was an excellent opportunity to reinforce his rule. To create more acceptance from the native Egyptians, Ptolemy IV shifted the location of the ceremony from the Macedonian capital Alexandria to Memphis, the ancient capital of Egypt.

Method The astronomical data as mentioned, have been calculated with the astronomical programs: 1. SkyMap Pro version 12, C.A. Marriott of SkyMap Software, United Kingdom. 2. Stellarium version 0.19.3. Stellarium is a free open source planetarium. It shows a realistic sky in 3D, what you see with the naked eye, binoculars or a telescope. The data of ancient Egypt have been converted with the online Data Converter for Ancient Egypt version 0.11 of Grieshaber, Seminar für Alte Geschichte und Epigraphik, Heidelberg, http://aegyptologie.online-resourcen.de/home. The selected date for the coronation is the 28th of November 205 BCE. That day coincides with the annual, last visible setting of Sirius. The phenomenon was visible in the early morning. At dawn, Sirius and all planets were visible, even Mercury. Most of the time, Mercury cannot be seen, because of its close proximity to the Sun. The Sun was an important symbol to the Egyptians and, as well as the Macedonians (Walbank, 2006). And so, the rising Sun emphasized the shared adoration of the Egyptian people and Macedonian ruler class. The last visible setting of Sirius fostered the benevolence of the native Egyptians. The setting of Sirius was a brief moment due to the imminent rising Sun. That exact moment was the time of the coronation of the king in Memphis around 6:10 local time. The calculation is based on an AMS (Robinson, 2009) at nautical twilight with altitude Sun -7° and altitude Sirius +2° (de Jong, 2006). In Commagene, Mt. Nemrud was an excellent location to observe the stars and keep track of the phenomena of Regulus. The Lion Horoscope is a stele of an ensemble of five at the West terrace of the mountain. The relief depicts a lion dotted with the stars of the constellation Leo. Regulus is depicted at the heart of the lion above the crescent moon. Above the back of the lion, the planets Mars, Mercury and Jupiter are depicted with their names inscribed above (Fig. 5). The relief displays the celestial configuration as seen from the West terrace on the 14th of July 109 BCE. This calculated day coincides with the annual, last visible setting of Regulus referred to as AES (Robinson, 2009). At dusk, Regulus, Saturn, Jupiter, Mars, and even Mercury were visible. Due to the imminent setting of Regulus in the west, the phenomenon was visible but for a brief moment (see Fig. 6). That was the time of the coronation of the king on the West terrace on Mt. Nemrud (Crijns, 2002). The time is calculated as 20:02 local time. The calculation is based on an AES at nautical twilight with altitude Sun -8° and altitude Regulus +0.5°.

• The Rosetta text (Ptolemaic Egypt) and the Nomos of Commagene follow a similar structure: introduction of the king, list of accomplishments, and detailed description of cult practices; both were displayed on steles throughout their realms and established annual and monthly celebrations for the king’s birthday and coronation. - Both kings identified with a star rather than a planet: the Ptolemies with the Sun as royal metaphor and Egypt’s marker star Sirius; Antiochus I with Regulus, the "royal star". - Astronomical reconstructions indicate that the coronation dates correspond to annual visibility phenomena of their respective marker stars: for Ptolemy V, the apparent morning setting (AMS) of Sirius on 28 November 205 BCE around 06:10 local time in Memphis; for Antiochus I (represented on the Lion Horoscope), the apparent evening setting (AES) of Regulus on 14 July 109 BCE around 20:02 local time at Mt. Nemrud. - In both configurations, multiple planets, including Mercury, were visible, and the Sun was positioned at a cardinal point, creating auspicious and publicly legible celestial displays. - The rarity of the Commagenian planetary configuration is emphasized: "That this specific planetary configuration [read: Lion Horoscope] can be found in the era of Commagene and not in any other era over a period of 10,000 years is unique and statistically significant' (Crijns, 2014). - The textual and astronomical parallels suggest that the Rosetta decree could have served as a blueprint for Antiochus’s Nomos, or alternatively, that both drew from a shared, older star-cult tradition.

The paper argues that astronomical phenomena were deeply embedded in ancient religious and political practice across civilizations. Understanding such practices requires at least basic astronomical literacy among archaeologists, echoing Sir Norman Lockyer’s call for archaeology to integrate astronomy. Archaeoastronomy provides valuable tools but broader familiarity is needed to interpret interconnections among Middle Eastern cultures. The observed textual and celestial parallels between the Ptolemaic and Commagenian cults may reflect either direct influence or a common heritage originating in earlier star cults of the Fertile Crescent.

The study identifies significant textual and astronomical similarities between the Rosetta decree of Ptolemy V and the Nomos of Antiochus I of Commagene. It reconstructs precise coronation timings tied to annual visibility phenomena of marker stars (Sirius and Regulus), shows that both cults institutionalized parallel festival cycles, and highlights the rarity of the Commagenian planetary configuration. These findings support either direct transmission from Ptolemaic Egypt to Commagene or a shared inheritance from older Near Eastern star cults. The paper underscores the need for expanded, in-depth archaeoastronomical research to map cultural interrelations across the Middle East and encourages broader astronomical literacy in archaeological interpretation.