Augustus’ solar meridian functioning and the birth of the western leap year
Abstract In 12 BCE, Augustus undertook the responsibility for the calendar, which had gradually fallen out of alignment with the true dates of solstices and equinoxes. Augustus’ calendar reform, entailing the introduction of a leap day every four years, coincided with the erection of a grand meridia...
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Nature Portfolio
2025-05-01
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| Online Access: | https://doi.org/10.1038/s41598-025-00653-8 |
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| author | V. Baiocchi M. Baumgartner M. Barbarella M. T. D’Alessio S. Del Pizzo F. Giannone F. Radicioni A. Stoppini G. Tosi S. Troisi L. Alessandri |
| author_facet | V. Baiocchi M. Baumgartner M. Barbarella M. T. D’Alessio S. Del Pizzo F. Giannone F. Radicioni A. Stoppini G. Tosi S. Troisi L. Alessandri |
| author_sort | V. Baiocchi |
| collection | DOAJ |
| description | Abstract In 12 BCE, Augustus undertook the responsibility for the calendar, which had gradually fallen out of alignment with the true dates of solstices and equinoxes. Augustus’ calendar reform, entailing the introduction of a leap day every four years, coincided with the erection of a grand meridian in the Campus Martius, known in Latin as Horologium Augusti. This device utilized the obelisk of Psamtik II (6° century BCE) as its gnomon that casted its shadow upon a travertine floor inscribed with bronze reference marks. Despite the discovery of the obelisk in 18th century and partial excavation of the floor in 1980, comprehending its geometric intricacies, regarding both dimensions and positioning, remained a challenge due to the complexities of conducting precise geomatic measurements in subterranean environments. Consequently, uncertainties persisted regarding its operational mechanics, particularly regarding whether the marks denoted days or ecliptic degrees. This study presents accurate measurements and statistically rigorous analyses that enable a precise repositioning of the meridian and a careful reconstruction of its geometry. The results suggest that the marks likely denoted specific days of the year, as recalled by Pliny the Elder. This provides support to the hypothesis that the monument functioned as an empirical validation of Augustus’ calendrical reform. In addition, the great accuracy achieved in positioning represents a fundamental aid in the desirable scenario to continue excavations of the meridian. |
| format | Article |
| id | doaj-art-66e66f150b9743d7812e7d1bf9807f15 |
| institution | Kabale University |
| issn | 2045-2322 |
| language | English |
| publishDate | 2025-05-01 |
| publisher | Nature Portfolio |
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| series | Scientific Reports |
| spelling | doaj-art-66e66f150b9743d7812e7d1bf9807f152025-08-20T03:48:05ZengNature PortfolioScientific Reports2045-23222025-05-0115111710.1038/s41598-025-00653-8Augustus’ solar meridian functioning and the birth of the western leap yearV. Baiocchi0M. Baumgartner1M. Barbarella2M. T. D’Alessio3S. Del Pizzo4F. Giannone5F. Radicioni6A. Stoppini7G. Tosi8S. Troisi9L. Alessandri10Sapienza University of RomeSoprintendenza speciale archeologia, belle arti e paesaggio di RomaUniversity of Bologna, DICAMSapienza University of RomeParthenope University of NaplesNiccolò Cusano UniversityUniversity of PerugiaUniversity of PerugiaUniversity of PerugiaParthenope University of NaplesSapienza University of RomeAbstract In 12 BCE, Augustus undertook the responsibility for the calendar, which had gradually fallen out of alignment with the true dates of solstices and equinoxes. Augustus’ calendar reform, entailing the introduction of a leap day every four years, coincided with the erection of a grand meridian in the Campus Martius, known in Latin as Horologium Augusti. This device utilized the obelisk of Psamtik II (6° century BCE) as its gnomon that casted its shadow upon a travertine floor inscribed with bronze reference marks. Despite the discovery of the obelisk in 18th century and partial excavation of the floor in 1980, comprehending its geometric intricacies, regarding both dimensions and positioning, remained a challenge due to the complexities of conducting precise geomatic measurements in subterranean environments. Consequently, uncertainties persisted regarding its operational mechanics, particularly regarding whether the marks denoted days or ecliptic degrees. This study presents accurate measurements and statistically rigorous analyses that enable a precise repositioning of the meridian and a careful reconstruction of its geometry. The results suggest that the marks likely denoted specific days of the year, as recalled by Pliny the Elder. This provides support to the hypothesis that the monument functioned as an empirical validation of Augustus’ calendrical reform. In addition, the great accuracy achieved in positioning represents a fundamental aid in the desirable scenario to continue excavations of the meridian.https://doi.org/10.1038/s41598-025-00653-8AugustusSolar meridianAncient RomeLeap yearCalendarLeast squares fit |
| spellingShingle | V. Baiocchi M. Baumgartner M. Barbarella M. T. D’Alessio S. Del Pizzo F. Giannone F. Radicioni A. Stoppini G. Tosi S. Troisi L. Alessandri Augustus’ solar meridian functioning and the birth of the western leap year Scientific Reports Augustus Solar meridian Ancient Rome Leap year Calendar Least squares fit |
| title | Augustus’ solar meridian functioning and the birth of the western leap year |
| title_full | Augustus’ solar meridian functioning and the birth of the western leap year |
| title_fullStr | Augustus’ solar meridian functioning and the birth of the western leap year |
| title_full_unstemmed | Augustus’ solar meridian functioning and the birth of the western leap year |
| title_short | Augustus’ solar meridian functioning and the birth of the western leap year |
| title_sort | augustus solar meridian functioning and the birth of the western leap year |
| topic | Augustus Solar meridian Ancient Rome Leap year Calendar Least squares fit |
| url | https://doi.org/10.1038/s41598-025-00653-8 |
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