Mural painting is inherently different from all other forms of pictorial art in that it is organically connected with architecture. The use of colour, design, and thematic treatment can radically alter the sensation of spatial proportions of the building. In this sense, mural is the only form of painting that is truly three-dimensional, since it modifies and partakes of a given space. Byzantine mosaic decoration evinced the greatest respect for organic architectural form. The great artists of the Renaissance, on the other hand, attempted to create an illusionistic feeling for space, and the masters of the subsequent Baroque period obtained such radical effects as to seem to dissolve almost entirely the walls or ceilings. Apart from its organic relation to architecture, a second characteristic of mural painting is its broad public significance. The mural artist must conceive pictorially a social, religious, or patriotic theme on the appropriate scale in reference both to the structural exigencies of the wall and to the idea expressed.