How did the workweek develop
The modern workweek, where there are five days of work and a two-day weekend, developed in the early 20th century as a response to religious observance and worker needs as the Industrial Revolution had begun to affect all aspects of life. Although the origins of the week, and even concepts of a weekend, are very old, only over the last 100 years has there been a formal, set concept of a workweek and weekend in many countries.
Early Origins
The origin of the 7-day week originate in ancient Mesopotamia, from Sumerian-Babylonian culture that likely developed about 5000 years ago. The Babylonians saw that 7 was a type of 'divine' number, with seven major planets and group of seven gods signifying aspects of the relevance for the number 7. This concept led them to divide time in weeks with 7 being the key division in a week. The names of the week were named after gods and this is also true in our modern system. Thursday, for example, was meant to be Thor's Day, that is the day of Thor in the Anglo-Saxon language.