Stained-glass windows have been admired for their utility and beauty since ancient Rome, when pieces of coloured glass were assembled into patterned window frames. In Europe, the art of stained glass reached its height between 1150 and 1500, when magnificent windows were created for great cathedrals. Techniques of stained glass window construction were described by the monk Theophilus who wrote a how to for craftsmen about 1100 AD.
As a material the term "stained glass" generally refers to glass that has been coloured by adding metallic salts during its manufacture. Painted details and yellow stain are often used to enhance the design. The term is also applied to windows in which all the colours have been painted onto the glass and then annealed in a furnace.
Stained glass, as an art and a craft, requires the artistic skill to conceive the design, and the engineering skills necessary to assemble the decorative piece, traditionally a window, so that it is capable of supporting its own weight and surviving the elements.
Although usually set into windows, the purpose of stained glass is not to allow those within a building to see out or even primarily to admit light but rather to control it. For this reason stained glass windows have been described as 'illuminated wall decorations'.
The design of a window may be non-figurative or figurative. It may incorporate narratives drawn from the Bible, history or literature, or represent saints or patrons. It may have symbolic motifs, in particular armorial.