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How Did the Days of the Week Get Their Names?

The days of the week are names you've known your whole life, but do you know their origin?

By
Samantha Enslen, Writing for
6-minute read
Episode #757
icons of days of the week
The Quick And Dirty

The days of the week are named after the sun, the moon, and a collection of Norse and Roman gods. Each week has seven days because ancient Babylonians thought there were seven planets in the sky, with each one controlling a different day of the week here on earth. Their method of tracking time never went out of style, and we still follow that same system today.

To talk about how we got the names of the days of the week, we have to go back in time—way back to 4000 BC, when the Babylonian civilization flourished in the Persian Gulf.

Ancient Babylonians First Divided the Year Into Weeks of Seven Days Each

Just as people have done throughout history, the Babylonians looked up to the sky. They tried to understand what was out there and how it might affect them. They could, of course, see the sun, and the moon, and the stars.  And rather amazingly, even without telescopes, they could see five planets—the five closest to Earth.   

And like everyone did until Copernicus came on to the scene in the 1500s, the Babylonians thought the Earth lay at the center of the universe, with everything else revolving around it. But the Babylonians also believed that we were intimately connected to the planets; that each planet ruled an individual hour of the day and an individual day of the week. 

Accordingly, they organized their life into a system of seven days, aligned to the seven celestial bodies they could see. The first two days of the week—our Sunday and Monday—were ruled by the Sun and the Moon. The next five were ruled by the planets. 

Notably, even back then, chilling the heck out was a thing. The Babylonians designated one day of the week as a day of rest. 

The Ancient Greeks Named the Days of the Week After Their Gods

Sometime around the 12th century BC, the ancient Greek civilization grew in prominence, and they adopted the Babylonian system of marking time. They continued to recognize the prominence of the sun and the moon, calling two days of the week hemera helio (day of the Sun) and hemera selenes (day of the Moon). Instead of naming the other five days after planets though, they named the days in honor of their gods. 

They named Tuesday for Ares, their savage god of war; Wednesday, for Hermes, the messenger of the gods, a trickster, and the god of commerce. Thursday they named for Zeus, god of the sky and thunder, and king of all other gods and men. Friday they named for Aphrodite, goddess of love. Saturday was named for Kronos, son of the creators of the universe, and the lovely guy who killed his father, ate his children, and was imprisoned by Zeus in Hades for being an all-around jerk.

The Romans Replaced the Names of the Greek Gods With Their Gods

Time kept on passing. In the first century BC, the Roman Empire began to emerge.  The Romans used the same seven-day system as the Greeks. And they considered the Greek gods to be the same as their own gods, simply called by different names. For example, the Romans looked at the Greek god of the sea, Poseidon, and were like, “Oh, that’s the same as our god of the sea, Neptune. He’s so powerful, people worship him everywhere, even though they call him by a different name.” 

Tuesday, they called dies Martis, replacing the Greek god of war Ares with their own god, Mars. Wednesday became dies Mercurii, with Mercury taking the place of Hermes. Thursday became dies Jovis, named for Jove (also known as Jupiter), the Roman equivalent to Greek head honcho Zeus. Friday became dies Veneris, named for Venus, the Roman’s version of Aphrodite, goddess of love.

For Saturday, perhaps feeling that Kronos was a challenging guy to honor, the Romans took a different tack. They named it for Saturn, father of Jupiter, god of agriculture, and namesake to the Saturnalia festival, a celebration in which masters and slaves traded places for a few wonderful days. 

The Romans continued the tradition of honoring the sun and the moon above all else, calling Sunday “dies Solis” and Monday “dies Lunae.” 

At least for a while. Emperor Constantine, a convert to Christianity, was concerned about ongoing worship of the sun and sun gods. So he changed the name of “Sunday” to “dominicus,” literally “the Lord’s Day.” He decreed that it should be the first day of the week, and a day of rest and worship.

The Anglo-Saxons Replaced the Names of the Roman Gods with Their Gods

Time continued to march on. At the end of the 4th century AD, the Roman Empire fell, and Anglo-Saxon tribes began their conquest of Britain and Wales. One way they made a mark on the world was by renaming the days of the week yet again, after—guess who?—their gods. 

Sunday, dies solis, became “Sonnandæg” in Old English. Monday changed from “dies Lunae” to Monandæg, as the Latin “luna” was swapped out for the Old English word for moon, “mōna.” 

Dies Martis became “Tiwesdæg,” as the Anglo-Saxons replaced the Roman god Mars with the Norse god Tyr, god of war and upholder of law and justice. Tyr was also known as “Tiu” or “Tiw,” which led to the name “Tiwesdæg”—and today’s “Tuesday.”

For Wednesday, the Anglo-Saxons decided to raise the whole thing another level. They replaced the trickster Mercury with Odin, the Allfather, creator of the universe, god of war, and god of poetry. Odin was also known as “Wodan,” which explains the odd spelling of this day of the week. In Old English, it was “Wodnesdæg”—literally—Wodan’s day.” Today, it’s Wednesday.

They named Thursday after everyone’s favorite Avenger: Thor, god of Thunder, and counterpart to the Roman Jupiter. 

For Friday, they replaced Venus with Freya (also known as Frigg or Frigga), sorceress, wife of Odin, and goddess of love and beauty. The Old English “Frigadæg” evolved over time into “Friday.”

Apparently the Anglo-Saxons were happy enough to honor a god of agriculture, because they continued to recognize Saturn on the last day of the week. In Old English, they called it “Saeternsdæge.” In other words, “Saturday.”

In sum, today we follow a seven-day week because that’s how ancient Babylonians thought the universe worked. And we call the days of the week after the sun, the moon, and a collection of Norse and Roman gods and goddesses.  

origins of days of the week

The Days of the Week in Other Languages Still Honor Roman Gods

One thing that's interesting is that the historical evolution we just described is apparent when you look at the days of the week in other languages too.

For example, in Roman times, Tuesday was called dies Martis, for the god Mars. The French and Spanish words for Tuesday reflect that: “mardi” and “martes,” respectively. 

Same with  Wednesday. The Romans named the day after Mercury. The French word for the day is “mercredi,” and the Spanish word is “miércoles.”

In any case, whenever you look at your calendar from now on, I hope you have a richer understanding of those simple words at the top. They link us with some of our early ancestors, and with myths that have circled the world for centuries. 

Image courtesy of Shutterstock.

Sources

Ancient History Encyclopedia. Saturn. https://www.ancient.eu/Saturn/ (accessed January 14, 2020).

Crowl, Lawrence A. The Seven-Day Week and the Meanings of the Names of the Days. https://www.crowl.org/Lawrence/time/days.html (accessed January 14, 2020).

Croy, N. Clayton. A God by Any Other Name: Polyonymy in Greco-Roman Antiquity and Early Christianity. Bulletin for Biblical Research 24.1 (2014) 27–43. 

Encyclopedia Britannica, online edition. Week, Roman Empire, Babylonia, Anglo-Saxons (subscription required, accessed January 14, 2020).

Encyclopedia Mythica. Origins of the names of the days. https://pantheon.org/miscellaneous/origin_names_days.php  (accessed January 14, 2020).

GreekMythology.com. Zeus, Ares, Aphrodite, Hermes. https://www.greekmythology.com/ (accessed January 14, 2020).

McCoy, Daniel. Norse Mythology for Smart People. Odin, Thor, Freya, Frigg. https://norse-mythology.org/ (accessed January 14, 2020).

Okrent, Arika. Where do the Days of the Week Get Their Names? https://www.youtube.com/watch?v=JEyuQd-zMeg (accessed January 14, 2020).

Oxford Classical Dictionary, online edition. Oxford University Press. Syncretism (subscription required, accessed January 14, 2020).

Oxford English Dictionary, online edition. Oxford University Press. Sunday, Monday, Tuesday, Wednesday, Thursday, Friday (subscription required, accessed January 14, 2020).

About the Author

Samantha Enslen, Writing for Grammar Girl

Samantha Enslen is an award-winning writer who has worked in publishing for more than 20 years. She runs Dragonfly Editorial, an agency that provides copywriting, editing, and design for scientific, medical, technical, and corporate materials. Sam is the vice president of ACES, The Society for Editing, and is the managing editor of Tracking Changes, ACES' quarterly journal.

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