There's a lot of sources on the internet which are happy to tell you that the Roman year originally had 10 months (Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, December) and provide more-or-less authoritative derivations for those names.

However, nothing I've found explains why four (later six) months were named for gods (mostly) and six were simply numbered. Do we have any explanation for what happened to Quartilis, Tresember, Duober, or Unilis? (pardon the butchery)

Related, why are some of the numbered months -ber and some -ilis? Is this just Roman grammar, or is there some other reason?

2 Answers 2


I couldn't find the source but once I read that the five gods naming the months were the most important gods in the Ancient Roman religion, before it received Celtic and Greek influences:

  • March - The first month named for a Father God, Mars. Mars was the most important god for the original Romans, because Romulus and Remus were their sons. And Jupiter means etymologically "Father Sky" (like Zeus means "God").

  • April - For a goddess of Love, Aphrodite.

  • May - For an Earth goddess, Maia, the ubiquos agricultural deity in all the Mediterranean ancient socities.

  • June - For a Mother Goddess, Juno.

So the four main aspects: father, mother, love and agriculture. Without marriages and children, a society don't last.

January was named for Janus, an Old God akin to Chaos.

January was named after Janus, a sky-god who was ancient even at the time of Rome’s founding. Ovid quoted Janus as saying "The ancients called me chaos, for a being from of old am I." After describing the world’s creation, he again quoted Janus: "It was then that I, till that time a mere ball, a shapeless lump, assumed the face and members of a god." http://www.webexhibits.org/calendars/calendar-roman.html

And February was probably named because it was the last month of the year and its name meant "purification", so they could expiate before starting the new year.


Note that the four godly months were full months of 31 days, with the remainder hollow and only 30 days. Why question are frequently impossible to answer, with reasons lost long past in antiquity. We are left to surmise that the naming scheme was chosen to reflect the length difference.

Yes, the stylistic differences are the result of the two forms being of different declension.

Here is a representative declension of the Latin noun September:
enter image description here and for comparison Junius:
enter image description here

For the uninitiated, a short primer on Latin noun declensions with English equivalents:

  • Nominative case is used for the subject of a sentence or clause, as in "September is a month", or as the object of the verb to be as in "The movie is Sweet November".
  • Genitive case is used for possessive phrases, where English would use "During the 30 days of September we ate no fish.".
  • Dative case is used for an indirect object of a verb (ie to or for something) such as "Julius Caesar gave an extra day to July in his calendar reforms".
  • Accusative case is used for normal direct objects of a verb and of most prepositions.
  • Ablative case is used for constructions that in English use the prepositions from, with, by, in and at, as in "Caesar took a day from February in his calendar reforms."
  • Vocative case is used for direct address and in English would be prefaced (whether implicitly or explicitly) by Oh, as in "Friends! Romans! Countrymen! I come not to praise Caesar but to bury him".
  • 1
    I can't actually make sense of what the two grammatical images are supposed to convey, and I was more asking about the Sextilius/September distinction, not the godly months. Also, the table on the Wikipedia link shows Aprilis and Junius with 30 days, and October with 31, so I don't think the godly=full,others=empty distiction holds up.
    – Bobson
    Jul 12, 2018 at 16:18
  • @Bobson: I have added a short Latin primer on noun declensions. Jul 12, 2018 at 16:37

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