Eleven interactive calendars rooted in classical astronomy and Mesopotamian, Egyptian, Persian, Hebrew, Arabian, Greek, Roman, Mesoamerican, and Byzantine timekeeping traditions.
Long before mechanical clocks, civilizations measured time through the sky. The Sumero-Akkadian world watched the first crescent above Babylon; the Pharaonic court anchored its year to Sirius rising over Memphis; pre-Julian Rome read days as fasti, comitiales, nefasti against the lunar Kalends and Ides. Each system encoded cosmology into calendrical structure — and each still rewards close reading.
The five tools below reconstruct these calendars with astronomical precision. Each is a standalone interactive instrument: pick a date, explore the month, read the deities and omens, and follow the original sources.
Twelve lunar months from Nisannu to Addaru, with the Akitu New Year festival at the spring equinox. Includes Iqqur ipuš hemerology, MUL.APIN heliacal risings, and Astrolabe B commentary.
Open Calendar →The 365-day civil year of three seasons — Akhet, Peret, Shemu — with the Cairo Calendar of Lucky & Unlucky Days, decans, Sothic cycle, and epagomenal feast days. Sourced from Papyrus Cairo 86637.
Open Calendar →12 months × 30 days + 5 Gatha days, with each day named after a Yazata (divine being), the six Gahānbar seasonal festivals, Nowruz, the Zurvan concept of infinite time, and three-thousand-year cosmic epochs. From the Avesta to the Sasanian era.
Open Calendar →12 months (plus Adar II), the Shalosh Regalim three pilgrimage festivals, Yamim Noraim (Days of Awe), Shemitah and Yovel land-cycles, the Metonic 19-year cycle, Hillel II's reform, and the Gezer Calendar.
Open Calendar →12 months, the manāzil al-qamar (28 lunar mansions), pilgrimage-season fairs (ʿUkāẓ, Majannah, Dhū al-Majāz), the nasīʾ intercalation debate, and the star catalog from the Muʿallaqāt suspended odes. Astronomy of the pre-Islamic pagan era.
Open Calendar →The Athenian calendar (12 months, prytany system), Hesiod's heliacal star catalog, the Panhellenic Games (Olympia, Pythia, Nemea, Isthmia), the Antikythera Mechanism, and the birth of Hellenistic astrology.
Open Calendar →The authentic Roman calendar before the 45 BC reform. Lunar Kalends, Nones, and Ides; day characters (F, N, NP, C, EN); and the priestly intercalation that wandered with the moon and pontifical decree.
Open Calendar →All eight Moon phases for any month, with zodiac transits, Moon-planet aspects, and classical agricultural guidance from Columella, Palladius, Pliny, Cato, and Varro. Generate a personal PDF.
Open Calendar →251 Sun-Venus conjunctions from 1900 to 2100, marking inferior (retrograde) and superior (direct) phases. Traces the pentagram pattern that returns near the same zodiac point every eight years.
Open Calendar →Tzolk'in (260 days), Haab' (365 days), 52-year Calendar Round, and 5125-year Long Count. Dresden Codex Venus table, the 9 Lords of the Night, and two-way Gregorian ↔ Mayan conversion. GMT 584283 correlation.
Open Calendar →Eastern Rome's time reckoning from Creation. Greek month names, the 15-year Indiction cycle, Eastern Easter computed on Julian dates, fixed liturgical feasts (Brumalia, Theotokos, Theophany) and astronomical events.
Open Calendar →A calendar is not only a way of counting days. It is a culture's argument about which days matter — which begin a year, which welcome a god, which forbid a journey, which favor a marriage. To read a Babylonian almanac is to inherit a civilization's sense of where the sky pressed most heavily on human life.
The earliest astrology grew directly from these calendars. The Mesopotamian month names became the zodiac. The Egyptian decans became the 36 segments of the hour-stars. The Roman religious year shaped what classical authors meant by "favorable" and "unfavorable" days. Even modern electional and horary astrology can be traced — line by line — back to entries in cuneiform menologies and hieratic papyri.
Each tool here is a living artifact: not a museum piece, but an instrument you can use today. Pick your birthday and read what the Babylonian priests would have said about it. Find your wedding date on the Cairo Calendar and see whether it falls on a "good, good, good" day. Watch the Roman lunar month unfold across thirteen Kalends-cycles instead of twelve. The texts have been waiting three thousand years for this kind of attention.
About ancient calendar systems
A calendar is more than a way of counting days — it is a culture's argument about which days matter. Mesopotamian month names became the zodiac; Egyptian decans became the 36 hour-stars; Roman fasti and nefasti days laid the foundation of electional astrology. To read these calendars is to touch the raw source of classical astrology.
The Babylonian calendar goes back to ~2000 BC (pre-Hammurabi), the Egyptian civil calendar to ~2700 BC. The Mayan Long Count starts in 3114 BC (mythological creation). The Roman calendar is nominally dated to 753 BC (Romulus). The Hebrew calendar represents the longest continuously living tradition — 3,500+ uninterrupted years.
A lunisolar calendar reconciles lunar and solar cycles: months are lunar (29-30 days), the year approximates the solar year (~365 days). The drift is corrected by intercalation (inserting a leap month). Babylonian, Greek, Hebrew, Roman, Mayan, Byzantine are lunisolar.
A pure lunar calendar follows only the Moon; it is not synced with the solar year and drifts back ~11 days per year. The Islamic Hijri calendar and the pre-Islamic Arab calendar (after nasīʾ was abolished) are fully lunar.
Yes. Every calendar tool (Babylonian, Mayan, Byzantine, Hebrew, Egyptian, etc.) provides two-way conversion between Gregorian and its own system. Enter your birth date and see the ancient equivalent — including the associated deity/star, festival context, and omens.
Yes — each calendar page is rooted in primary and secondary academic sources. Examples: MUL.APIN and Astrolabe B tablets for Babylonian; Papyrus Cairo 86637 (Lucky & Unlucky Days) for Egyptian; Fasti Antiates Maiores inscription for Roman; Dresden Codex for Mayan; Censorinus and Justinianus documents for Byzantine.
VSOP87 (planets) and ELP2000 (Moon) ephemerides are used — the modern astronomical standard. All key events (spring equinox, full moon, heliacal rising, solstice) are computed at arcsecond precision. For historical calendars, proleptic Julian and Sothic calibration are applied.
This page (the Calendars Hub) gives card-based access to all 11 calendars. Each card has a description and an "Open Calendar" CTA. You can also reach the same hub from the Tools page by clicking the "📅 Calendars" filter button.