Why We Have a Seven Day Week and the Origin of the Names of the Days of the Week

days-of-the-weekToday I found out why we have a seven day week and the origins of each day’s name.

Two of the earliest known civilizations to use a seven day week were the Babylonians and the Jews.  The Babylonians marked time with lunar months and it is thought by many scholars that this is why they chose a seven day week (though direct evidence of this being why they did this is scant). That being said, each lunar month was made up of several different cycles—on the first day, the first visible crescent appeared; on approximately the seventh, the waxing half-moon could be seen; on approximately the fourteenth, the full moon; on approximately the twenty-first, the waning half-moon; and on approximately the twenty-eighth, the last visible crescent. As you can see, each notable cycle is made up of about seven days, hence, the seven-day week.

You’ll notice I used the word “approximate” a lot in there.  This is because the moon phases don’t line up perfectly with this schedule.  As such, as far back as the 6th century BC (which incidentally is also around the time the Jews were captives in Babylon), the Babylonians would sometimes have three seven day weeks, followed by an 8-9 day week, presumably to re-synchronize the start and end of the weeks to match the phases of the moon.

In their normal seven day week, the Babylonians held the seventh day of each week as holy, much like the Jews did and still do.  However, the Babylonians also held the day to be unlucky.  Thus, similar to the Jews (but for a different reason- the unluckiness of the day), the seventh day had restrictions on certain activities to avoid dire consequences from the inherit unluckiness of the day. The final “seventh day” of the month for the Babylonians was a day of rest and worship.

By deistic decree, the Jews also followed a seven day cycle with the seventh day- the Sabbath-  to be a day of rest and worship.  In fact, the word “Sabbath” comes from the Hebrew “shabbath”, meaning “day of rest”, which in turn comes from the Hebrew “shabath”, meaning “he rested”- thus resting in homage to God resting on the seventh “day” after creating the universe. (Note: some biblical scholars believe the “day” here, in terms of six “days” to create the universe, one to rest, is more accurately translated as “period” or “interval” rather than a literal Earth day.  This is perhaps not unlike the “40 days and 40 nights” Jewish saying being a non-literal ancient Jewish expression simply meaning “a really long time”.)

Unlike the Babylonians, where it appears they were attempting to follow the lunar cycles with their seven day week, it isn’t known why the Jews picked seven days, outside of Christians and Jews of course believing that it was by the decree of God.

Whatever the case, the Ancient Romans, during the Republic, did not use a seven day week, but rather went with eight days.  One “eighth day” of every week was set aside as a shopping day where people would buy and sell things, particularly buying food supplies for the following week.

Rather than labeling the days of the week with actual names, at this time the Romans labeled them with letters, A-H.  You might think from this that the “H” was always the shopping day, but this isn’t correct.  You see, the calendar year did not divide evenly by eight.  Thus, the day of the week that was the day to go shopping changed every year, but they still often referred to days based on its proximity to the shopping day.

For reasons not entirely clear, within a century after the introduction of the Julian Calendar was introduced in 46 BC, the eight day week started to diminish in popularity in favor of the seven day week.  The full switch was not sudden, happening over centuries, and for a time, as the seven day week grew in popularity, both the seven and eight day weeks were used in Rome simultaneously.  Finally, after the popularity of the eight day week diminished to almost nothing, Constantine, the first Christian Roman Emperor, made the seven day week official in AD 321.  Due to the influence of both Rome and Christianity, this has stuck in most regions of the world ever since.

So now what about the origins of the names of the days of the week?  Ancient Mesopotamian astrologers assigned each day the name of a god. The Greeks later called these days “theon hemerai”, or if that’s all Greek to you, “days of the Gods”. In a culture where days were consumed by religion, it’s only natural that the days of the week were made in homage to the gods thought to rule the lives of mortals. The days of the week follow the same trend as the months of the year, many of which (including January and March) are named after gods from several different pantheons.

The Romans, upon beginning to use the seven day week instead of the eight day, then adopted the names of the week to fit their own gods. The names of the week were then adopted by Germanic peoples. Despite Greek and Roman gods being the more popular and more well-known of the pantheons, it is largely the Germanic and Norse gods that have received the most credit and live on in the names of the days of the week today.

While different societies start the week on different days—usually Sunday or Monday—I’ll start with Monday, which was named for the moon. It could be translated as “Moon’s day”. This homage to the moon can be seen in several other languages as well. In Latin, it’s “dies lunae”, or “day of the moon”. In ancient Greek, “hemera selenes”, which means the same thing. In more modern languages, Monday is “lunes” in Spanish and “lundi” in French, both of which come from the root word for moon—”luna” and “lune” in each respective language.

Tuesday is the first to be named after a god. It was named for Tiu, or Twia, a lesser-known god of war and the sky from the English/Germanic pantheon. He is also associated with the Norse god Tyr, who was a defender god in Viking mythology. However, Tuesday does not translate the same in other languages. In Latin, it’s “dies Martis” or “Day of Mars” and in ancient Greek it’s “hemera Areos” or “day of Ares”. Both Mars and Ares were gods of war like Tyr and they lent their names to day of the week translations for other modern languages. Tuesday is “martes” in Spanish and “mardi” in French, both named for the Roman god Mars.

Wednesday can be translated as “Woden’s day”. Woden, associated with the Norse god Odin, was the chief god and leader of the wild hunt in Anglo-Saxon mythology. Directly translated, “woden” means “violently insane headship”, and does not put one in mind of the best of gods. Unlike the other days of the week, the gods named in the Latin and Greek days of the week – Mercury and Hermes —  are not associated with violent leadership, but with travel, commerce, and theft. Both are messenger gods. It is for Mercury that Spanish and French decided to name Wednesday—”miercoles” and “mercredi” respectively.

Thursday is one of the easiest days to translate, meaning “Thor’s day”. Named for the Norse god of thunder and lightning. Thursday is also associated with Jupiter in Latin (“dies Jovis”) and Zeus in Greek (“hemera Dios”). All three gods are known for their storm-creating abilities, but while the English language took Thor as its god for Thursday, Spanish and French adopted Jupiter instead, naming Thursday “jueves” and “jeudi” which have roots in Jupiter.

Friday is associated with Freya, the Norse goddess of love, marriage, and fertility. The Latin, “dies Veneris”, and the Greek, “hemeres Aphrodite”, call upon the goddesses Venus and Aphrodite instead. The latter two goddesses are also patrons of love and beauty, and all three goddesses are called upon in womanly matters like fertility and childbirth. Following the trend of the other days, Spanish and French adopted Venus for Friday rather than Freya, naming their days “viernes” and “vendredi”.

Saturday in English derives from “Saturn’s day” which was taken from the Latin, “dies Saturni”. Saturn was a Roman god and, over different periods of time, associated with wealth, plenty, and time. The day in Spanish and French (“sabado” and “samedi” respectively) was named simply as it is the Jewish Sabbath- “sabado” deriving from the Latin “sabbatum”, meaning “Sabbath”, and “samedi” deriving from the Old French “samedi”, which in turn comes from the Latin “dies Sabbati”, meaning “Day of the Sabbath”.

Sunday is “Sun’s day”, translated in both Latin (“dies solis”) and Greek (“hemera helio”) as “day of the sun”. Interestingly, in Spanish and French (“domingo” and “dimanche”) it is more closely translated as “Lord’s day” or “Sabbath day”, pointing to more the Christian/Jewish God.

If you liked this article, you might also like:

Bonus Facts:

  • For a very brief time in France, the French abandoned the seven day week in favor of a ten day week, beginning in 1793 thanks to the new republican calendar developed in France at that time.  This was abandoned nine years later when the Roman Catholic Church was reestablished in France.  The official switch back to the seven day week happened on April 18, 1802- Easter Sunday.
  • The USSR also for a time (starting in 1929) abandoned the seven day week in favor of at first a five day week, then a six day week.  This in turn was abandoned and the seven day week was re-established in 1940.
  • One complete lunar phase cycle, a “lunation”, is currently exactly 29 days, 12 hours, 44 minutes, and 3 seconds.
  • The Latin days of the week also reflect those planets closest to Earth—Mercury, Venus, Mars, Saturn, and Jupiter, plus the sun and moon.
  • Sunday is a working day in many Muslim countries and Israel. It is also a popular day in the United States and the United Kingdom to schedule televised sporting events.
  • Monday is considered a bad day because it is the first day of the working week, but in Judaism and Islam, it is considered a good day for fasting. It is also a day to commemorate angels in the Eastern Orthodox Church.
  • In the United States, Labor Day, Memorial Day, Columbus Day, and Veteran’s Day always fall on Mondays.
  • In Greek tradition, Tuesday is considered unlucky because Constantinople fell on a Tuesday. In Judaism, Tuesdays are lucky because in the Book of Genesis it is mentioned as a good day twice.
  • Wednesdays are days for fasting in the Eastern Orthodox Church.
  • In Australia, most shopping malls have “late night shopping” on Thursdays, as it is the day most Australians are paid.
  • Friday is considered an unlucky day to begin a voyage, but a good day for sowing the seed. Condemning a slave on Friday is forbidden under Muslim law.
  • Saturday is the Jewish day of rest, rather than Sunday as is common in most denominations of Christianity.
[Days of the Week Image via Shutterstock] Expand for References
Share the Knowledge! facebooktwittergoogle_plusredditpinteresttumblrmailfacebooktwittergoogle_plusredditpinteresttumblrmail
Print Friendly
Enjoy this article? If so, get our FREE wildly popular Daily Knowledge and Weekly Wrap newsletters:

Subscribe Me To:  | 


  • What a badly-written article. It’s so bad that reading it and trying to make sense of it will actually damage your brain.

    “it isn’t known why the Jews picked seven days”

    Oy. The Babylonians and the ancient Jews did not just happen to both have 7-day weeks with the 7th day being holy. The Babylonians were excellent astronomers and the Jews adopted the 7-day week from them during their Babylonian captivity.

    As for the names of the days of the week, try this simple explanation:

    The Latin names, based mostly on the names of Roman gods, continued to be used in the languages derived from Latin – Italian, Spanish, and French.

    The Anglo-Saxon tribes who conquered Britain and helped create the English language substituted the names of their gods for the Latin names.

    There, I fixed it for you.

    • Daven Hiskey

      @ganesh: “The Babylonians and the ancient Jews did not just happen to both have 7-day weeks with the 7th day being holy. The Babylonians were excellent astronomers and the Jews adopted the 7-day week from them during their Babylonian captivity. ” While that was my initial inclination too, it turns out there is no hard evidence of that, just circumstantial. The Jews and Christians, of course, will argue that the 7 day week among the Jews has been around since Moses, which predates 6th century Babylon by a good margin. Bottom line, if there is no hard evidence, I can’t have such a definite assertion made in an article on TIFO. As you see in the article, it was noted that around the first evidence of the Babylonian 7 day calendar, the Jews were in Babylon, hinting at the connection. But, again- to put it in explicitly we’d need some hard evidence. If you know of some, please share.

      “As for the names of the days of the week, try this simple explanation.” You see, that doesn’t make a very interesting article. TIFO’s all about the details and impeccable accuracy in them. If you want that kind of simplistic explanation, lacking interesting details, you should check out a site like OMGFacts or the like. Granted, there you’ll find a lot of inaccuracies, but they have gotten a bit better about that the last year or two- still can be sketchy though.

      “What a badly-written article.” For the reasons listed above, and that it’s incredibly hard to write an article with a list of etymologies and the like and still maintain great readability and flow (so that it doesn’t start reading like a dictionary), I’m going to have to strongly disagree with you on that one. Everybody’s got their own tastes, but I thought this was a phenomenally written article and was much more interesting than I thought it would be from the base topic, which usually means the author did a great job. Particularly for a second time TIFO article effort from this author, Emily, I am actually a little blown away at how good it is. :-)

  • “Sabado” does not mean Saturn; it means “Sabbath”. The Sabbath is the seventh day of the week, which is Saturday, and to this day, Jews keep it on the seventh day.

  • But why was Saturday named for a Roman god rather than an Anglo-Saxon/Norse god? Did the Norse use a 7-day week? Or was it 6 days, accounting for having to import a name from Latin?

    • Daven Hiskey

      Nobody knows exactly why a Roman god was picked, though it’s speculated that it was simply because there was no corresponding Northern European Saturn god, so they just stuck with what the Romans used.

      The Old Norse name for the day was “laugardagr”, literally meaning “bath day”. :-)

  • The names of the days of the week in East Asia are very similar, down to the corresponding planets – http://en.m.wikipedia.org/wiki/Week-day_names#East_Asian_Seven_Luminaries

    When I took Japanese language classes years ago I particularly noticed the parallels with Sunday and Monday.

  • You mention that Tuesday is the first day to be named after a god implying that the sun and the moon were not gods. You also mentioned that these traditions come from the Babylonian (actually it’s Sumerian before them) and in Babylon, the sun and the moon WERE associated with gods – Shamash and Sin. The sun is still called Shamash in Hebrew, Arabic and other Semitic Languages. I know the wikipedia article – http://en.wikipedia.org/wiki/Seven-day_week – mostly mentions Babylon, however, the Babylonians were using the system they got from Sumer. As far as we can tell, the Sumerians were the ones who assigned the days of the week and the gods they are associated with. Also, the reason there are 60 seconds in a minute and 60 minutes in an hour is because the Sumerians used a numbering system known as Sexagesimal – http://en.wikipedia.org/wiki/Assyro-Babylonian_mathematics. There are many books talking about how many facets at the very core of of our current civilization started in Sumer.

    To me, the fact that there are only seven objects that wander in the sky and that there are seven days, each associated with a wanderer (and as you mention, associated with the same exact ones to this day) is a pretty big coincidence.

  • The name of the first day of the week has names such as Domenica and Domingo in Catholic countries and replaced ‘Day-of-the-sun’ which was the day dedicated to the god Mithras. This took place when Constantine adopted Christianity as the roman religion.

  • Dude, as an israeli i promise you that sabbath doesn’t mean “the day of rest”. shabbat or as you call it, sabbath comes from the verb “lashevet” which means to sit. i’m sure you can see the coonnection how that means to rest.

    • Daven Hiskey

      @Ori: Sources? Online etymology dictionary and Oxford both say “from the Hebrew ‘shabbath’, meaning ‘day of rest'”.

  • The information fails to recognize India’s contribution. Kalidasa composed Shakuntala & Dushyanata play/drama around 600 BCE, many centuries before Shakespeer of 17th Century. Scholar Kautilya (Chanakya) of Chandraguta Maurya’s dynasty around 300 BCE wrote Artha Shastra Economics & Politics. Western scholars fail to recognize India’s contribution, gives credit only to Egyptians, Babylon & Jews etc. India’s Aryan & Dravidian culture & civilization is the oldest & surviving civilization. India had ancient Takshashila & Nalanda International Universities Vishva Vidyalaya. Muslim invaders destroyed India’s many valuable historical important structures, Takshshila University, currently located in Pakistan & Nalanda university in Bihar/Orissa state. Harappa &Mohenjadaro civilization is one of the oldest & richest.Ancient. Ancient Indians were using 7 days in a week, each day of the week named after a plant of our Solar system, except for Mondaya , named after earth’s Satllite Moon, instead of a Planet.

    • Sitaram Rudrapattana – Do you have any specific source establishing that “7 day week” concept was used prior to British rule?

  • In modern Israeli Hebrew, “shavat” means “he struck [went on strike]”.


  • i’m curisous about the friday definition. The German name for it, Freitag, meaning the Free Day. I’m pretty sure with both German and English being Germanic language that they have the same etymology, thus friday meaning the free day and not reffering to Freya

    • The original norse day name was Frjádagr
      My guess would be that the reassemblance to “Freeday”of the German one, derives from the differences of spelling:
      Freja (Danish/Swedish) = Fre-dag
      Freia/Freiya (German) = Frei-tag

  • My Thought was
    (One’s day) was turned to sunday or Monday
    (two’s day) was turned to Tuesday
    (Four’s day) was turned to Thursday
    (Five day) was turned to Friday

  • My thought was

    (We’d like to get over this hump) Wednesday

  • The Mesopotamians invented the 7-day week ca. 700 BC. They Made Saturn’sday the first day because the considered Saturn to be the top god.

    As the convention spread, Saturday remained the first day until Constantine transferred that honor to Sun’sday because the sun was more widely worshipped in the west.

    Np pre-Constantinian calendar has ever been found that had Saturday as the 7thday of the week, even among Jews, who had no calendar weeks in their culture. Only after Saturday became the 7th day in the fourth century did the Jews began to associate the “7th day” in the sabbath commandment with the 7th day of the week ( instead of merely whatever day happened to follow 6 days of work)

    Even if the Jews had kept an unbroken 7-day cycle before Constantine, (they didn’t), it took the insertion of a single 6-day week to move Saturday from the first day to the seventh day. So much for an unbroken chain of 7-day weeks back to Moses or creation.

  • Veteran’s Day is not Always on a Monday. It is always observed on the eleventh day November. This is done to stay consistent with the signing of the documents that ended World War Two. It sign on the 11th day of the 11th month at 11:11 AM. Thus it is ALWAYS observed November 11th.

  • The seven day week comes from the seven days of creation and the Sabbath, the 7th day was Sabbath as spoken by God, our creator. This occurred long before Israel and the Jews were appointed by God.

    • I see that everyone has their own version of the making of our planets 7 day cycle, one has stated it to be a God, although which one of the many that were around 2,015 years ago.
      Prior to the ‘Virgin Mary’ what was the religion of the peasants she would socialise with. Obviously not Christianity.

  • Also interesting

    Why are there 12 months in the year?
    Julius Caesar’s astronomers explained the need for 12 months in a year and the addition of a leap year to synchronize with the seasons.
    At the time, there were only ten months in the calendar while there are just over 12 lunar cycles in a year.
    The months of January and February were added to the calendar
    The original fifth and sixth months were renamed July and August in honor of Julius Caesar and his successor Augustus.
    These months were both given 31 days to reflect their importance, having been named after Roman leaders.


    Rule – 30 days has September, April, June and November
    9 + 4 + 6 +11= 30

  • Have none of you read the Holy Bible – Chapters 1 and 2? – The ancient cultures stemmed from the same source, carried the same information. There is God, who claim he founded the 7 day week, and established at the end of his 6 days work, a day for resting, unbounded by the evening and the morning.
    Whatever Babylonian was in place, when the captured the Jews, and instilled them into their society the result for the prime king, Nebuchadnezzar, was the uptaking of the creator God as learned from the Jew named Daniel/Belteshazzar.

  • Have you looked into why ancient india had seven days? a week was called ‘saptah’ which translates to collection of seven.
    Also check the time this came up.. perhaps after babylonians or at the same time.

  • Can any one tell When onwards Hindu adopted the week days? There is no reference of week days such as Sunday,Monday..etc.Not even mentioned in Tamil THIRUKURAL about it

Leave a Reply

Your email address will not be published. Required fields are marked *