There are several possible origins of the 7-day week. Though one of them is biblical, the seven-day week was established long before Christianity.

For instance, the ancient Babylonians’ week had seven days, each of them dedicated to a different deity. The Babylonians associated the seven heavenly bodies normally visible to the naked eye (the Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn) with a deity.

The names of the days of the week have different meaning in different languages.

For example, Jews simply number their week days (except for the Sabbath). The similar method is partially used in Portuguese and some Slavonic languages (Russian). Most Latin-based languages, however, connect days of the week with one of the seven planets of the ancient times (French uses lundi (Moon), mardi (Mars), mercredi (Mercury), jeudi (Jupiter), vendredi (Venus), samedi (Saturn)).

Now the seven-day week is a conventionally used time unit, adopted by all religions and cultures. However, there is difference of opinion as to what day is to be regarded as the first day of the week. While Jews and Christians regard Sunday as the first day of the week, some modern calendars end the week on Sunday and begin it on Monday (because of the two-day weekend). The international standard ISO 8601 also defines Monday as the first day of the week.

History of the week