When and why were stained glass windows first incorporated into the design of a Christian place of worship?

Many Christian churches incorporate stained glass windows into their design. Some members have noted that the use of stained glass windows in architectural design pre-dates Christianity. That being said, I'm more concerned with their incorporation into Christian architecture, which I assume would have been done first by Orthodox Christianity or Roman Catholicism. 1. What denomination or branch of Christianity first incorporated stained glass windows into their places of worship? 2. Why were stained glass windows used (aside from the common utility of a window), and why are they still used today? 3. Is there a Church tradition that they *must* be used in the design of a church?