M - Category
A picture or decorative design made by setting small colored pieces, as of stone or tile, into a surface.0 A decoration created by setting small pieces of glass, stone, or marble in a matrix- often concrete. Wall mosaics were most prevelent in the Early Christian and Byzantine periods, during which they were a very important form of wall decoration.
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The vertical element that separates the lancets of a window. It can also be the vertical member separating adjacent windows. Or simply it can be the horizontal and vertical bars separating window lights (glass).