A study suggests that a Lusitanian jewel from the Chão de Lamas treasure is key to understanding the astronomical cycles of the Celts

A recent study published in the journal Palaeohispanica has revealed a new perspective on ancient timekeeping systems. The research, conducted by Professor Roberto Matesanz Gascón from the University of Valladolid, proposes that the lunula with geometric decoration from the Chão de Lamas treasure (Portugal) could contain information about the synchronization of lunar and solar cycles in the Celtic calendar.

The lunula, a piece of goldsmithing in the shape of a half-moon that was part of a treasure found in Chão de Lamas (Miranda do Corvo, Coimbra), has traditionally been considered a decorative object. However, the analysis of its intricate geometric patterns suggests that it could be a visual record of a Celtic calendrical cycle spanning a period of 114 years. According to Matesanz, this period corresponds to six Metonic cycles (each lasting 19 years), an astronomical pattern that allows the lunar calendar to align with the solar calendar.

The Coligny calendar, found in France and dating from the 2nd century AD, is the most detailed epigraphic source about how the Celts organized time. This record divides time into five-year cycles of 62 months, totaling 1,835 days. However, scholars have debated for decades how these periods synchronized with the tropical year of 365.24 days.

lunula geometric celtic calendar
Detail of the lunula and nomenclature of the circular motifs present in it. Credit: Piero Baguzzi / R. Matesanz / MAN, Ministerio de Cultura de España

What is innovative about Matesanz’s study is that it establishes a link between the Coligny calendar and the decoration of the Chão de Lamas lunula. According to his hypothesis, the circular motifs on the jewel would represent a time-keeping scheme in which, every 114 years, the difference with the solar year was adjusted by eliminating 53 days. This figure of 53 days also appears in Irish literary sources, suggesting a possible connection with the Celtic tradition of Ireland.

Geometric Symbols and Their Relation to Celestial Cycles

The design of the lunula is not merely ornamental. Matesanz identifies in it a series of large concentric circles and small circles with central dots, distributed across five main sections. In his analysis, the researcher notes that these elements could correspond to the months of the five-year cycle of the Celtic calendar.

The key lies in the numerical arrangement of these motifs. According to the study, the geometric elements of the lunula seem to represent six five-year cycles, each with 62 months. The total sum of these months results in a span of 30 years, the so-called Celtic saeculum, mentioned by Pliny the Elder in his Natural History. But here arises the problem: this calculation leaves an excess of 53 days when compared to the actual solar cycle.

The solution, according to the researcher, would have been the elimination of those days in the calendar adjustment every 114 years. This adjustment would have allowed festivals and astronomical events to remain aligned with the seasons.

lunula geometric celtic calendar
The Coligny calendar. Credit: Public domain / Wikimedia Commons

A Link to Irish Mythology

The most intriguing aspect of the research is that the figure of 53 days appears in texts from the Irish Gaelic tradition, specifically in the medieval tale Baile in Scáil. In this story, the legendary king Conn Cétchathach steps on a magical stone on the Hill of Tara, but his druids tell him they cannot reveal his name until 53 days have passed. This period of time with no information or action could correspond to the days that were eliminated in the Celtic calendar to maintain its alignment with the solar year.

If this hypothesis is confirmed, it would demonstrate that Celtic oral tradition preserved, even centuries after Romanization, remnants of an ancient method of synchronizing time. This would reinforce the idea that the Celtic civilization had advanced astronomical knowledge, reflected both in their artifacts and in their mythology.

The study also raises questions about the use of art as a symbolic language. In this regard, the Chão de Lamas lunula could be a testament to how the Celts embodied abstract and mathematical concepts in their artistic creations.

lunula geometric celtic calendar
The Leiro Helmet. Credit: Carlos de Paz / Wikimedia Commons

Other archaeological finds support this idea. In the Iberian Peninsula, objects with similar iconography have been found, such as the Axtroki bowls or the Leiro helmet, whose decoration also suggests a possible calendrical function. In Central Europe, objects like the Schifferstadt-type golden hats have been interpreted as instruments for timekeeping.

SOURCES

Roberto Matesanz Gascón, La lúnula con decoración geométrica del tesoro de Chão de Lamas y el calendario celta. Palaeohispanica, vol.24 (2024). doi.org/10.36707/palaeohispanica.v24i1.543

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