Under the reign of Shah Jahan, the symbolic content of Mughal architecture reached a peak.[23] The Taj Mahal complex was conceived as a replica on earth of the house of the departed in paradise (inspired by a verse by the imperial goldsmith and poet Bibadal Khan.[note 2][8] This theme, common in most Mughal funerary architecture, permeates the entire complex and informs the detailed design of all the elements.[24] A number of secondary principles also inform the design, of which hierarchy is the most dominant. A deliberate interplay is established between the building's elements, its surface decoration, materials, geometric planning and its acoustics. This interplay extends from what can be experienced directly with the senses, into religious, intellectual, mathematical and poetic ideas.[24] The constantly changing sunlight reflected from the Taj's translucent marble is not a happy accident, it had a deliberate metaphoric role associated with the presence of god as light.[25]
Symmetry and hierarchy[edit]
Symmetry and geometric planning played an important role in ordering the complex and reflected a trend towards formal systematisation that was apparent in all of the arts emanating from Jahan's imperial patronage. Bilateral symmetry expressed simultaneous ideas of pairing, counterparts and integration, reflecting intellectual and spiritual notions of universal harmony. A complex set of implied grids based on the Mughul Gaz unit of measurement provided a flexible means of bringing proportional order to all the elements of the Taj Mahal.[26]
Hierarchical ordering of architecture is commonly used to emphasise particular elements of a design and to create drama. In the Taj Mahal, the hierarchical use of red sandstone and white marble contributes manifold symbolic significance. The Mughals were elaborating on a concept which traced its roots to earlier Hindu practices, set out in the Vishnudharmottara Purana, which recommended white stone for buildings for the Brahmins (priestly caste) and red stone for members of the Kshatriyas (warrior caste). By building structures that employed such colour-coding, the Mughals identified themselves with the two leading classes of Indian social structure and thus defined themselves as rulers in Indian terms. Red sandstone also had significance in the Persian origins of the Mughal empire where red was the exclusive colour of imperial tents. In the Taj Mahal the relative importance of each building in the complex is denoted by the amount of white marble (or sometimes white polished plaster) that is used.[24][27]
The use of naturalist ornament demonstrates a similar hierarchy. Wholly absent from the more lowly jilaukhana and caravanserai areas, it can be found with increasing frequency as the processional route approaches the climactic Mausoleum. Its symbolism is multifaceted, on the one hand evoking a more perfect, stylised and permanent garden of paradise than could be found growing in the earthly garden; on the other, an instrument of propaganda for Jahan's chroniclers who portrayed him as an 'erect cypress of the garden of the caliphate' and frequently used plant metaphors to praise his good governance, person, family and court. Plant metaphors also find common cause with Hindu traditions where such symbols as the 'vase of plenty' (Kalasha) can be found.[28]
Sound was also used to express ideas of paradise. The interior of the mausoleum has a reverberation time (the time taken from when a noise is made until all of its echoes have died away) of 28 seconds. This provided an atmosphere where the words of those employed to continually recite the Qu'ran (the Hafiz), in tribute and prayer for the soul of Mumtaz, would linger in the air.[29]