Why the Week Hides Seven Gods (and Two Impostors)

You say "mardi" (or "Tuesday") without a second thought. Yet every time, you're summoning the Roman god of war. The days of the week are an old pantheon fossilised on your tongue, a pagan calendar that survived centuries of Christianity without anyone bothering to tidy it up. Which is a good thing, because the story is delicious.

It all starts with a simple idea from the astronomers of antiquity: up in the sky, seven bodies move against the fixed stars. The Sun, the Moon, and five wandering points of light they called planets (from the Greek planêtês, "the wanderer"). Those five had already been christened by the Romans with the names of their gods: Mars, Mercury, Jupiter, Venus, Saturn. Seven heavenly bodies, seven days. The circle was complete, and the planetary week spread across the whole Empire.

Five gods still standing

In Latin, people said Lunae dies, the day of the Moon. Let the pronunciation slide a little across the centuries, drop the ending, and you get lundi. The recipe is the same for the whole week.

Martis dies, the day of Mars, gives mardi. Mercurii dies, the day of Mercury the messenger, becomes mercredi (mind the hidden "r", that's where it comes from). Jovis dies, the day of Jupiter, or Jove, contracts into jeudi. And Veneris dies, the day of Venus, goddess of love, boils down to vendredi.

Five days, five deities, a logical thread that hasn't budged in two thousand years. If you want to shine at a party: the final "di" in all these words is simply dies, "the day", shunted to the end by usage. Our medieval ancestors flipped the Latin formula around, which had put the day first.

The two that betrayed Rome

That leaves Saturday and Sunday, and here things get tricky. Because in the original Roman system, those two days belonged to Saturn and the Sun. In English they stayed put: Saturday keeps Saturn intact, and Sunday remains the Sun's day. The French, on the other hand, did some housekeeping.

The culprit is Christianity. For the early Christians, the day of the Sun could hardly go on bearing the name of a pagan star: it had to be dedicated to the Lord. In Church Latin, dies Solis became dies dominicus, "the Lord's day" (from dominus, the master, the lord). From dominicus, French drew dimanche. It's the only day of the French week that speaks neither of a star nor of an ancient god, but of faith.

As for samedi, it comes from somewhere else again. Not from Rome, but from Jerusalem. The word descends from the popular Latin sambati dies, itself from sabbatum, the Hebrew sabbath, that day of rest inherited from Jewish tradition. Two days at the tail end of the week, two religious influences, one Christian, one biblical, that shoved Saturn and the Sun out the door.

The same sky, different gods

The most elegant part is the comparison with English, because you can watch a superb act of translation take place. The Germanic peoples took over the Roman week, but they swapped each Latin god for its local equivalent.

Look at the run of correspondences. Mars, god of war, gives way to Tiw (or Týr among the Norse), a warrior god: there's Tuesday. Mercury, the cunning messenger, becomes Woden, that is Odin: Wednesday (which even English speakers pronounce swallowing half the letters). Jupiter, master of thunder, hands his lightning to Thor: Thursday, Thor's day. And Venus, goddess of love, passes the baton to Frigg, Odin's wife: Friday.

Put another way, when you set a French calendar and an English one side by side, you're looking at the same Roman astronomical skeleton, dressed in two different mythologies. The planets are identical; only the names of the gods change depending on who was holding the pen.

This is the kind of detail that sleeps inside a general-knowledge question and can win you a whole round. Next time someone asks where "Wednesday" comes from, you won't recite a definition: you'll tell the tale of Mercury, the wandering planets, and two thousand years of linguistic habit. The rest of the table will go on believing the week was always there, flat and featureless, with no story at all.