Sunday is a Holiday

Where you might say? Generally, a holiday is used to describe any day additional to your normal days off. Is this what we are talking about? What makes Sunday a holiday? In A.D. 321, it was Emperor Constantine who decreed that the seven-day week was the official Roman week and made ‘Sunday’ a public holiday. He commanded that all work should cease on that day (Sunday). So why have we given up our holiday?