The Latin Names for Days of the Week

Roman days were named after planets, which had gods' names

RomanRepublic/Wikimedia Commons/Public Domain

Romans named the days of the week after the seven known planets, which had been named after Roman gods: Sol, Luna, Mars, Mercury, Jove (Jupiter), Venus, and Saturn. As used in the Roman calendar, the gods' names were in the genitive singular case, which meant each day was a day "of" or "assigned to" a certain god.

  • dies Solis, "day of the Sun"
  • dies Lunae, "day of the Moon"
  • dies Martis, "day of Mars" (Roman god of war)
  • dies Mercurii, "day of Mercury" (Roman messenger of the gods and god of commerce, travel, thievery, eloquence, and science.) 
  • dies Iovis, "day of Jupiter" (Roman god who created thunder and lightning; patron of the    Roman state) 
  • dies Veneris, "day of Venus" (Roman goddess of love and beauty)
  • dies Saturni, "day of Saturn" (Roman god of agriculture)

The Influence on Modern Romance Languages and English

Below is a table demonstrating the influence of Latin on English and modern Romance languages' names for days of the week. The table follows the modern-day European convention of beginning the week on Monday. The modern name for Sunday is not a reference to the ancient sun god but to Sunday as the Lord's Day or the Sabbath. 

Latin French Spanish Italian English
dies Lunae
dies Martis
dies Mercurii
dies Iovis
dies Veneris
dies Saturni
dies Solis

A Little History of Latin Days of the Week

The official calendars of the ancient Roman Republic (from about 500 BC to 27 BC) don't show the days of the week. By the Imperial Period (from 27 BC to about the end of the fourth century AD) that changed. The fixed seven-day week was not widely used until the Roman Emperor Constantine the Great (306–337 AD) introduced the seven-day week into the Julian calendar. Prior to this, the Romans had lived according to the ancient Etruscan nundinum, or eight-day week, which set aside an eighth day for going to the market.

In naming the days, the Romans emulated the earlier Greeks, who had named the days of the week after the sun, the moon and the five known planets. Those heavenly bodies had been named after Greek gods. "The Latin names of the planets were simple translations of the Greek names, which in turn were translations of the Babylonian names, which go back to the Sumerians," says scientific researcher Lawrence A. Crowl. So the Romans applied their names for the planets, which had been named after these Roman gods: Sol, Luna, Mars, Mercury, Jove (Jupiter), Venus, and Saturn. Even the Latin word for "days" (dies) is said to derive from the Latin "from the gods" (deusdiis ablative plural). 

Sunday (Not Monday) Began the Week

On the Julian calendar, the week began on Sunday, the first day of the planetary week. This could be a response "either to Jewish and then Christian influence or to the fact that the Sun had become the principal Roman state god, Sol Invictus," says Crowl. "Constantine did not refer to Sunday as 'the Lord's Day' or 'the Sabbath,' but as the day celebrated by veneration of the sun itself (diem solis veneratione sui celebrem). "[So] Constantine did not abruptly abandon the solar cult despite his establishment of Christianity." 

It could also be said that the Romans named Sunday as the first day based on the sun being "the chief of all the astral bodies, just as that day is the head of all the days. The second day is named for the moon, [because it] is closest to the sun in brilliance and size, and it borrows its light from the sun," he says.

"The curious thing about the Latin [day] names, clearly using the planets, is that [they reflect] the ancient order of the planets, rising from the Earth to the Fixed Stars," adds American philosopher Kelley L. Ross. 

-Edited by Carly Silver