The interior chamber of Taj Mahal steps far beyond traditional decorative elements. Here the inlay work is not pietra dura, but lapidary of precious and semiprecious gemstones. The inner chamber is an octagon with the design allowing for entry from each face, though, only the south garden-facing door is used. The interior walls are about 25 metre high and topped by a "false" interior dome decorated with a sun motif. Eight pishtaq arches define the space at ground level. As with the exterior, each lower pishtaq is crowned by a second pishtaq about midway up the wall.
The four central upper arches form balconies or viewing areas and each balcony's exterior window has an intricate screen or jali cut from marble. In addition to the light from the balcony screens, light enters through roof openings covered by chattris at the corners.
Each chamber wall has been highly decorated with dado bas relief,
intricate lapidary inlay and refined calligraphy panels, reflecting in miniature
detail of the design elements seen throughout the exterior of the complex.
The octagonal marble screen or jali which borders the cenotaphs is made from eight marble panels. Each panel has been carved through with intricate piercework. The remaining surfaces have been inlaid with semiprecious stones in extremely delicate detail, forming twining vines, fruits and flowers.
Muslim tradition forbids elaborate decoration of graves and hence Mumtaz and
Shah Jahan are laid in a relatively plain crypt beneath the inner chamber with
faces turned right and towards Mecca.
Mumtaz Mahal's cenotaph is placed at the precise center of the inner chamber with a rectangular marble base of 1.5 metre by 2.5 metre. Both the base and casket are elaborately inlaid with precious and semiprecious gems.
Calligraphic inscriptions on the casket identify and praise Mumtaz. On the
lid of the casket is a raised rectangular lozenge meant to suggest a writing
tablet. Shah Jahan's cenotaph is beside Mumtaz's to the western side. It is the
only visible asymmetric element in the entire complex.
His cenotaph is bigger than his wife's, but reflects the same elements: A larger casket on slightly taller base, again decorated with astonishing precision with lapidary and calligraphy that identifies Shah Jahan. On the lid of this casket is a traditional sculpture of a small pen box.
The pen box and writing tablet were traditional Mughal funerary icons decorating men's and women's caskets respectively. Ninety Nine Names of God are to be found as calligraphic inscriptions on the sides of the actual tomb of Mumtaz Mahal, in the crypt including "O Noble, O Magnificent, O Majestic, O Unique, O Eternal, O Glorious... ". The tomb of Shah Jahan bears a calligraphic inscription that reads; "He traveled from this world to the banquet-hall of Eternity on the night of the twenty-sixth of the month of Rajab, in the year 1076 Hijri."