The Taj Mahal mausoleum stands at one end of the garden adorned with fountains and marble pavements. The garden contains four water channels to echo the four rivers of the Islamic Paradise. It rises from a platform 313 ft (95 m) on a side, bearing a white marble minaret at each corner; the enclosure, 186 ft (57 m) on a side, has truncated corners and a high portal on each side. The white marble exterior is inlaid with semiprecious stones arranged in Arabic inscriptions (designed by a local artist Amanat Khan, who was Shah Jahan's calligrapher), floral designs, and arabesques, and the salient features of the interior are accented with agate, jasper, and colored marbles. The roofing dome, on the inside, is 80 ft (24.4m) high and 50 ft (15.2 m) in diameter; outside it forms a bulb, which tapers to a spire topped by a crescent. The tomb chamber, with its two sarcophagi, is an octagonal room in the center of the edifice (the royal couple, however, are buried in an underground vault). The chamber is softly illuminated by the light that passes through double screens of intricately carved marble set high in the walls.