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Gods in the calendar: weekdays and months
The short answer
English weekday names come from the Roman planetary week with Germanic gods swapped in for five of the seven days. Four of the month names are tied to gods or deified rulers by the Roman calendar page, and others stay uncertain. Of fourteen entries below, four are Attested, nine Scholarly and one Popular claim.
The weekday table is the more solid half. The reference page documents a Roman day name for each day, and Tacitus is the one ancient writer on the pages who names a Germanic god in Roman terms.
The week
The weekday page says many languages name the days after the seven classical planets, which were named after Hellenistic deities. It attributes the system to the Sumerians, later adopted by the Babylonians and then by the Romans in late antiquity, and presents the Babylonian origin as the majority view of historians. Most historians agree the seven-day week dates to about 4,000 years ago. The days follow the planets in the order Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn.
| Day | Latin | Greek god | Germanic | What the sources record | Strength | Source |
|---|---|---|---|---|---|---|
| Sunday | diēs Sōlis (Sun) | Greek Helios | Sunna, Old English Sunnandæg | A graffito at Pompeii dated 6 February 60 AD is the earliest evidence of dies solis as Sunday. Romance languages later changed the name to the Lord's Day. | Attested | Wikipedia: Names of the days of the week |
| Monday | diēs Lūnae (Moon) | Greek Selene | Máni, Old English Mōnandæg | The page's table pairs the Latin, Greek and Old English names. The Moon is the planet, and Máni is the Germanic moon figure. | Scholarly | Wikipedia: Names of the days of the week |
| Tuesday | diēs Mārtis (Mars) | Greek Ares | Tiw or Týr, Old English Tīwesdæg | It says the Germanic name is related to the Latin diēs Mārtis and does not call it a direct equivalence. | Scholarly | Wikipedia: Names of the days of the week |
| Wednesday | diēs Mercuriī (Mercury) | Greek Hermes | Woden or Óðinn, Old English Wōdnesdæg | The weekday page links Woden to Mercury as deities of magic and knowledge and as guides of the dead. Tacitus identifies the chief Germanic god with Mercury, which the Interpretatio page suggests may mean Wotan. | Attested | Wikipedia: Names of the days of the week, Interpretatio graeca |
| Thursday | diēs Iovis (Jupiter) | Greek Zeus | Thor or Þórr, Old English Þunresdæg | It presents the match as a correspondence and ties Thor to thunder. | Scholarly | Wikipedia: Names of the days of the week |
| Friday | diēs Veneris (Venus) | Greek Aphrodite | Frigg, Old English Frīgedæg | It says the Norse name for the planet Venus is Friggjarstjarna and discusses no alternative identification. | Scholarly | Wikipedia: Names of the days of the week |
| Saturday | diēs Sāturnī (Saturn) | Greek Cronus | None; Saturn kept, Old English Sæturnesdæg | Germanic peoples replaced the Roman gods with their own for every day except Saturday. Spanish sábado comes from the Sabbath. | Scholarly | Wikipedia: Names of the days of the week |
The entry gives dates for the Roman side. The Pompeii graffito of 6 February 60 AD is the earliest evidence of dies solis as Sunday. Plutarch wrote a lost treatise, around 100 AD, on why the planetary day names are in a different order from the planets' actual order. Constantine made the seven-day week official in AD 321, and by the fourth century it was in wide use across the empire. The Germanic adoption must have occurred after 100 AD and before Christianity arrived in the 6th or 7th century, and the exact date is unknown.
What the Germanic swaps rest on
The Interpretatio entry defines interpretatio romana as Roman comparative discourse about religion and myth, with Gallo-Roman religion as an example. It records that Tacitus first used the phrase in the Germania. He says a sacred grove of the Nahanarvali honored gods that in Roman terms were Castor and Pollux, and he identifies the chief Germanic god with Mercury, which the page suggests may refer to Wotan. The entry does not cover the weekday equivalences or a date for their adoption.
That leaves the Germanic names resting on the weekday page's own account. It says Tiw's name is related to the Latin day of Mars. It links Woden with Mercury through magic, knowledge and the guiding of the dead. It matches Thor with Jupiter through thunder and bases Friday on the Latin day of Venus. These are comparisons made by the page and not statements by an ancient writer, apart from Tacitus on Mercury.
Other languages follow the same week. Chinese adoption was possibly by the 4th century AD, with the Jin astrologer Fan Ning cited as evidence, and that the diaries of Fujiwara no Michinaga show it in use in Japan by 1007. Spanish keeps the Roman names for Monday through Friday (lunes, martes, miércoles, jueves, viernes), while domingo comes from Latin Lord's Day and sábado from the Sabbath.
The months
Roman calendar is a first organized year of ten fixed months, attributed to Romulus, the legendary first king, though some scholars doubt it existed. Four months had 31 days (March, May, Quintilis and October) and six had 30 (April, June, Sextilis, September, November and December), which totals 304 days. The two to three months of winter were left unorganized. Numa Pompilius is credited with dividing winter into January and February, which created a lunisolar calendar. Quintilis, Sextilis, September, October, November and December are archaic adjectives formed from the ordinals five through ten, which matches their positions when the year began at the March equinox.
| Month | Named for | Tradition | What the sources record | Strength | Source |
|---|---|---|---|---|---|
| January | Janus, god of beginnings and transitions | Roman | Ianuarius comes from Janus. Numa is credited with adding January and February, and Plutarch gives a version in which Numa moved them to the start of the year. | Scholarly | Wikipedia: January, Roman calendar |
| March | Mars | Roman | January and March honor the gods Janus and Mars. March was originally the first month. | Scholarly | Wikipedia: Roman calendar, January |
| April | Apru or aperire | Etruscan or Latin | It says April may relate to the Etruscan goddess Apru or to the verb aperire, to open, and marks this as unverified. | Popular claim | Wikipedia: Roman calendar |
| May | Maia or maiores | Roman | May may honor Maia or derive from an archaic term for senior. The entry leaves both open. | Scholarly | Wikipedia: Roman calendar |
| June | Juno or iuniores | Roman | June may honor Juno or derive from an archaic term for junior. The entry leaves both open. | Scholarly | Wikipedia: Roman calendar |
| July | Julius Caesar, not a god | Roman | Quintilis, Caesar's birth month, was renamed July in his honor after his assassination, on the page's account by Mark Antony. | Attested | Wikipedia: Roman calendar |
| August | Augustus, not a god | Roman | The plebiscite Lex Pacuvia de Mense Augusto renamed Sextilis in 8 BC. | Attested | Wikipedia: Roman calendar |
February may derive from the Februa festival or the word februa, meaning purifications, and the page calls its exact origin uncertain, so it appears in no row. The January entry adds only that Janus is the god of beginnings and transitions and notes the Saxon name Wulf-monath, wolf month, and Charlemagne's Wintarmanoth, winter month.
Where the evidence is thin
The Roman calendar page marks the April etymology as unverified. The weekday page tags Plutarch's answer on the order of the planetary days and the claim that Greek astrology existed from about the 2nd century BC as needing a citation. This article follows the pages and nothing more.
Julius Caesar and Augustus are rulers, not gods, and are included because their names sit beside the god names in the same calendar and because the page shows the same naming habit applied to people.
What the strength marks mean
Attested means a dated inscription, a named writer or a recorded legal act makes the match: the Pompeii graffito for Sunday, Tacitus for Mercury, and the Lex Pacuvia and the renaming of July. Scholarly means a reference page makes the comparison with the limits it gives. Popular claim means the page marks the origin as unverified.
The ancient texts were read through reference pages only. The Interpretatio entry does not cover the weekday equivalences, so that part rests on the weekday page.