7 day week is not a concept borrowed from Romans as it is generally believed. The 7 day week is not really based on western calendar. Firstly, lets look at how classic predictions ( Jyothisha Shastra ) of the Vedas for answers to these questions: Why do we have only 7 days in a week? Why can't we have 8 or 9? �What is an hour? �Why do we have only 24 hours in a day? Why can't we have 30 or 40 units and call it an hour?