Decoration 
Exterior decoration
Calligraphy on large pishtaq
Nearly every surface of the entire complex has been decorated. The exterior decorations of the Taj are among the finest to be found in Mughal architecture of any period.
Once again, decoration motifs are repeated throughout the complex. As the surface area changes -- a large pishtaq has more area than a smaller -- the decorations are refined proportionally.
The decorative elements come in basically three categories:
Calligraphy
Abstract geometric elements
Vegatative motifs
Islamic strictures forbade the use of anthropromorphic forms.
The decorative elements were created in three ways:
Paint or stucco applied to the wall surface
Stone inlay
Carvings