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.


What denomination or branch of Christianity first incorporated stained glass windows into their places of worship?
Why were stained glass windows used (aside from the common utility of a window), and why are they still used today?
Is there a Church tradition that they must be used in the design of a church?
Architecturally, Gothic churches required large trusses in order to support the ceiling.  This would make the buildings very dark. That said, the spaces between the trusses could be turned into windows in order to lighten the area.

Since the 400s, Mosaics had already been used both as art and as teaching tools. (See Ravenna for some of the best!) Combining the need for light with the established tradition of mosaics would have been a natural technological progression.