The authentic Roman calendar before the Julian reform (pre-45 BC). Months begin with the first sighting of the new crescent moon, Nonae corresponds to the first quarter, Idus to the full moon. Complete with day qualities (Fasti, Nefasti, Comitialis), festivals and cosmological layers.
The calendar we use today does not require us to look at the sky to track time. Days are fixed, months are fixed, the year is fixed... But Rome's oldest calendar was different. When the first crescent of the moon appeared on the western horizon, the pontifex would call out to the people from the Capitoline Hill, proclaiming the new month. This moment was Kalendae, and the word 'calendar' itself derives from this (calare = to call out, to proclaim). When the first quarter appeared in the sky came Nonae, when the full moon shone came Idus. Time was the rhythm of the heavens upon the earth.
In 45 BC, Julius Caesar's reform severed this connection. Months acquired fixed lengths, Kalendae no longer corresponded to the actual new moon but to the first day of the month, Idus no longer fell on the full moon but on the 13th or 15th of the month. The names remained but their celestial connections ended. Our modern calendar is the heir of this rupture.
I reconstructed this calendar to revive the system from before that rupture. The Roman calendar is one of the most important calendars we have for understanding astrology. Day qualities (Fasti, Nefasti, Comitialis), Dies Ater rules and festivals were compiled from Fasti Antiates Maiores (84-55 BC, the only surviving republican calendar), Macrobius, Ovid and Scullard. What you see here is not a literal copy of the historical Roman calendar. The old calendar depended on the political decisions of the pontifex maximus and cannot be precisely calculated today. This reconstruction is a working model of the era when sky and time had not yet been severed from each other.
In the Roman calendar, days were not expressed using a modern numbering system but through a countdown from three fixed reference points. Kalendae (the 1st day of the month) was the day the pontifex proclaimed the new crescent to the people ('calare' = to call out). Nonae corresponded to the first quarter, Idus to the full moon. This tool returns Kalendae/Nonae/Idus to their astronomical foundation by calculating actual moon phases.
Dies Fasti (F): Courts open, legal business permitted. Dies Nefasti (N): Courts closed, religious ceremonies take priority. Dies Comitialis (C): Popular assembly may convene. NP: Public festival, work avoided. EN: Split day: morning nefastus (sacrifice preparation), midday fastus, evening nefastus again. Dies Ater: The day after Kalendae, Nonae and Idus was considered inauspicious; new ventures were not begun.
Rome did not have a 7-day week; instead, an 8-day market cycle called Nundinae (A-H) was used. The year totaled 355 days, approximately 10 days shorter than the solar year. To compensate, in some years a 22-23 day intercalary month called Mercedonius was inserted after the 23rd day of Februarius. However, this decision rested with the pontifex maximus and could involve political motives.
This tool is an astronomical reconstruction of the pre-Julian Roman calendar. Since the historical Roman calendar depended on the decisions of the pontifex maximus, it cannot be precisely calculated. What is shown here is the calendar as it was designed.
Works that served as sources for this calendar reconstruction: Fasti Antiates Maiores (84-55 BC); Macrobius, Saturnalia; Ovid, Fasti; Varro, De Lingua Latina; Censorinus, De Die Natali; Ioannes Lydus, De Mensibus; Michels (1967); Scullard (1981).