Continuing my meditations on the names of the days of the week in English and French, which I began in my post Saturday and samedi, it occurred to me to wonder why we have weeks of seven days at all.
It seems that the seven-day week was probably settled by the Babylonians about 4,000 years ago. They might have chosen this rather awkward prime number seven for the length of the week for two reasons. The first is that the number seven was sacred to them – a vague memory of which perhaps still persists today when people think of the number seven as “lucky”. The second reason has to do with astronomy.
The Babylonians were accomplished mathematicians and also avid sky-watchers who virtually invented the science of astronomy. Their calendar defined the year as twelve synodic (lunar) months, making it about 354 days long. To reconcile it with the solar year used in agriculture, they added extra days as necessary.
The Babylonians were meticulous at record-keeping and this in itself enabled them to make a number of discoveries. For example, they discovered the Saros cycle of the moon. This lasts for about 18 years, 11 days and 8 hours during which lunar events recur almost exactly. Thus they were able to predict lunar and solar eclipses long before they actually happened.
The Babylonians knew that while the stars remained in fixed positions, there were certain celestial objects that moved. These included occasional visitors such as comets and meteors but the most important ones were the sun, the moon and the five known planets, Mars, Mercury, Jupiter, Venus and Saturn, or to give them their Babylonian names (in the same order), Shamash, Sin, Nergal, Nabû, Marduk, Ishtar and Ninurta. What would be more natural for these gifted astronomers than to name the seven days of the week after these seven celestial bodies which they associated with their gods?
The Greeks and the Romans took over this ancient week of seven days, substituting their own day names. The Romans named the celestial objects after their own gods and goddesses. The sun and the moon were seen as deities in their own right while the planets were designated as Mars, the god of war; Mercury, the messenger of the gods but also the god of commerce; Jupiter or Jove, in ancient times the god of the sky and thunder but to the Romans the chief of the gods with a propensity for casting down thunderbolts on people who angered him; Venus, the goddess of love and beauty; and Saturn, the god of sowing and agriculture in whose honour the festival called Saturnalia was held every year on December 17th.
The Romans took their calendar with them to the lands that they conquered and occupied. This included Britain but, whereas France and other old colonies of Rome continued using (and modifying) the Latin language and the Roman day names, in Britain, invading Scandinavian and Germanic tribes replaced the Romans and took over as the ruling class. Their language and culture became dominant. This of course affected, among other things, the names of the days of the week. Exactly how it affected them we shall see in due course. The seven-day week, however, was retained and is with us still.



