It's biblical. Saturday is the sabbath, the 7th day rest day, which would make sunday the first day. Later, christians decided to hold mass on sunday instead, b

It's biblical. Saturday is the sabbath, the 7th day rest day, which would make sunday the first day. Later, christians decided to hold mass on sunday instead, because it was when Jesus resurrected. Eventually you end up with saturday and sunday as rest days, even though one is biblically the first and one is biblically the last day of the week. But both are the "weekend".