Stained glass was unknown in antiquity. Invented around AD 1000, it soon achieved a dominant position in the arts of the Middle Ages, not only in churches but also in secular contexts. Its innovation can be compared with that of television - and like television it involves passing light through a transparent layer, using the light of sun instead of light generated by electricity, so that in a real sense the stained glass image is in constant motion, as the light passing through it changes.