This is the art of illusion ( BETRAYING THE EYES ). Started at the cave age and re-created in Rome and Egypt to give the impression of a open or large space using decorative paintings on walls reproducing: fake doors, arches, windows, balconies, designs representing wars, open sky ceilings etc. France and Italy ( Vatican: Fresco and France: Tromp ) gave to this kind of decorative art a new meaning. It was a symbol of power and wealth.
It was at that time and it is until today!
More affordable but eternally a symbol of beauty, good taste and power.