Why are there seven days in a week?

(Top left to bottom right) (L) Sun, Saturn, Moon, wolf, lightning, rhinemaiden, Venus di Milo

A week made up of seven days is part of our modern global culture, but its origins date back to ancient civilisation.

The Greeks gave us democracy, the Romans bridges and roads but it is probably from the ancient Babylonians that we get the seven-day week.

Living in the cradle of civilisation, Mesopotamia – modern Iraq, their culture was most prominent in the second and first millennia BC before the rise of Greece or Rome.

They were formidable astronomers and developed a calendar to plot and predict the movement of the moon and planets in the heavens, incorporating a form of astrology.

But while the movement of Earth and Sun give us natural concepts like days and years and the Moon’s phases give us the month, there is no such natural reason for a seven-day week.

The number seven had a mystical significance to Babylonians. It was associated with the seven heavenly bodies; the Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn.

For this reason, some believe, marking rituals every seventh-day became important. A seven-day week based on these same celestial bodies was adopted as far away as Japan and ancient China.

Seven is also important in Judaism, where the creation story is told over seven days. But unlike other cultures, in Hebrew the days of the week are assigned numbers not the names of gods, festivals, elements or planets – the only exception is Saturday, Yom Shabbat (יום שבת) which means Sabbath.

But the popularity of the seven-day week – and its prominence in modern calendars – can be traced to its adoption by the Romans.

They named the days of the week after the pagan gods of Rome, the Sun and the Moon.

Roman Emperor Constantine formally adopted the seven-day week in AD 321, it had been in use informally since the first century BC. A Christian convert Constantine made Sunday – the Christian Sabbath – the first day of the week, and Saturday – the Jewish day of rest – as the last.

For many though the week begins naturally with the first working day.


Half moon

Old English Mōnandæg, Latin dies lunae

The English word Monday comes from Old English and is named after the Moon and the moon-god, Máni who is the brother of Sunna, the Sun goddess in Norse mythology.

The early Anglo-Saxons who settled in England, were a warrior culture who worshipped pagan gods similar to those of the Nordic pantheon.

The Latin word for moon, luna may not give us the word for Monday but it does give us the modern English words lunar, lunatic and lunacy – a condition which has been associated in popular culture if not reality with the cycle of the Moon.

In Roman mythology Diana, the twin of Apollo the Sun-god, is the goddess of the moon, the hunt and child birth. Diana has the power to talk to and control animals.



Old English Tīwesdæg, Latin dies Martis

The English word Tuesday is also derived from Old English and from the Norse god of war Tiw (or Týr). The Latin Tuesday, dies Martis is named after Mars, the Roman god of war.

“The Anglo-Saxons naturalised Tuesday to Friday,” explains Professor John McKinnell, professor of medieval literature at Durham University, by using “the old Germanic gods that corresponded to the same Roman gods”.

Tiw (or Týr) was one of the sons of Woden, the supreme Norse deity. Týr was a war god but he is more often associated with the formalities of war – including treaties, as well as justice.

He is usually shown with only one hand. In the most famous myth about Týr he placed his hand between the jaws of the wolf Fenrir as a mark of good faith while the other gods, pretending to play, bound the wolf. When Fenrir realised he had been tricked he bit off Tyr’s hand.


Saxon re-enactors

Old English Wōdnesdæg, Latin dies Mercurii

Wednesday comes from Woden, the Old German and English name for the Norse god Odin.

Odin is father and ruler of the gods and mortals, often called ‘the all father’. He is also the god of war, learning, poetry and the dead.

He has only one eye, having traded his second for a drink from the Well of Wisdom.

He is the ruler of Asgard, the home of the gods, and is able to shift and change into different forms. In contrast Mercury, the Roman god for whom dies Mercurii is named, is a messenger god.

While Woden survives in English, he disappeared from the German days of the week. This dates from the time Christianity was displacing pagan beliefs in the centuries following the collapse of the Roman Empire.

“In Germany they found themselves the heirs to classical Rome as the Carolingian leaders of the Holy Roman Empire, so along with Christianisation went a willingness to embrace all that that new title meant.” explains archaeologist Iain Sodden.

In German, Wednesday or Woden’s day was replaced with Mittwoch or ‘mid-week’.



Old English Þūnresdæg, Latin dies Iovis

Thursday recalls Thunor (Þunor), the Anglo-Saxon name for the Norse god Thor.

In Latin records, Thor is associated with both the chief Roman god Jupiter who gives his name to the Latin Thursday dies Iovis and the Greek demi-god Hercules.

Red-headed Thor ruled the skies, storms and thunder, which is still named after him. He had iron gloves, a magic belt and his hammer Mjölnir.

During the Christianisation of Scandinavia in the 10th and 11th Centuries emblems of Thor’s hammer Mjölnir, were worn by pagans as a symbol of defiance against the new religion.

In Iceland, Bishop Jon Helgi Ogmundarson went on a mission to eradicate any remaining pagan beliefs or trace of them.

So the ‘day of Odin’ became ‘mid-week-day’ and the days of Týr and Thor became respectively ‘third day’ and ‘fifth day’.

After 1066, Anglo-Saxon speakers in England were cut off from their medieval German cousins and the English language was isolated from some European influences – resulting in pagan references remaining in the language which disappeared elsewhere.


(L)Two musicians playing Rhinemaidens in Wagner's Ring Cycle (R) Venus de Milo

Old English Frīgedæg, Latin dies Veneris

Friday is named after the Norse goddess Frigg (also called Friia), the wife of Odin, who represents love and beauty. She is also associated with marriage and fertility.

Frigg’s star or Friggjarstjarna was the Nordic name for Venus, which can outshine any of the other planets.

Venus was the Roman goddess of love, beauty, sex, fertility, prosperity and victory. Venus was closely associated with the Greek goddess Aphrodite.

Frigg was the wife of Odin and queen of the gods which means she is more akin to the Roman Juno (the wife of Jupiter) as a figure. The Roman Venus may have more in common with another Norse goddess Freyja who is associated with love, beauty, fertility, gold, war, and death.



Old English Sæturnesdæg, Latin dies Saturni

Saturday is the only English week-day still associated with a Roman god, Saturn.

Saturn was the Roman god of fertility, agriculture and time. He is the father of Jupiter, the chief Roman god, and associated with wealth and abundance. The Temple of Saturn was in the Forum of ancient Rome which housed the state treasury.

The association of Saturday with a Roman god in English helps date when the seven-day week came to Britain.

According to Prof Mckinnell it suggests that the names of the days “may have arrived in the UK along with Latin learning – with or after the conversion to Christianity, between AD 597 and AD 685.”

In the Romance languages of southern Europe which are largely derived from Latin, the word for Saturday was changed to mirror Church Latin. For example the Spanish word sábado comes from Sabbath.

In Danish the name for Saturday Lørdag has nothing to do with any god, Roman, Nordic or Christian. It simply means wash-day or bath-day.


Sun rise over water

Old English Sunnandæg, Latin dies Solis

The English Sunday is of course named after the Sun, as is the Roman equivalent.

Many societies have worshipped the sun and sun-gods. Perhaps the most famous is the Egyptian Sun-god Ra, who was the lord of time. Ancient Egyptians believed that all forms of life were created by Ra, who called each of them into existence by speaking their secret names. Ra is also the Coptic word for sun.

In many languages the pagan name for Sunday was changed for a Christian one. The Italian word for Sunday, Domenica, means ‘of the Lord’ and in Russian voskresen’je (воскресенье) means ‘resurrection’.

This change never happened in English, probably because of a division in language between different classes after the Norman invasion of 1066.

“While the official Norman-French language in use amongst the lordly elite switched effortlessly into official Latin and used the ‘Lord’s Day’, Anglo-Saxon remained the vernacular of ordinary folk,” Mr Sodden told the BBC.

The seven-day week records our pagan past but it also comes to us from Judean and Christian tradition and the creation story in Genesis, the first book of the Old Testament.

The earliest ancient sources record a seven-day week in ancient Babylon prior to 600 BC. At that time the Jewish people were enslaved and exiled there for generations and no doubt were operating to the same seven-day period.

A millennium later, Emperor Constantine the Great converted Rome to Christianity and standardised the seven-day week across the Empire.

According to Dr Matthew Nicholls, senior lecturer in Classics at the University of Reading: “The Roman context of the spread of Christianity meant that Rome contributed a lot to the structure and calendar of the new faith.”

Rome may initially have acquired the seven-day week from the mystical beliefs of Babylonian astrologers. But it was the biblical story of creation, God making the Heavens and Earth and resting on the seventh day that will have led the first Christian emperor of Rome to make sure it endured to this day.