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.
While what was the Sumerian-Babylonian concept of week eventually influenced the Hebrew calendar and later the Western calendar through adoption in the Classical world, the idea of a workweek had not developed fully in the ancient world. Among the closest, however, was the Jewish use of the weekly calendar, where there would be six days of work and one Sabbath day based on the interpretation that God created the world in six days and rested on the seventh. This did influence what became the Christian week, where the Sabbath was effectively Sunday. In the Medieval period in Europe, people were expected to work throughout the week and on Sunday worship in their local perish.