The Moti Masjid ("Pearl Mosque") is the main mosque within the Agra Fort complex. Constructed by Shah Jahan towards the end of his reign, its white marble cladding gives it a reflective pearly hue, while its simplicity regarding ornament contrasts with the more elaborately decorated red sandstone buildings of the fort complex.

The mosque is located north of the Diwan-i 'Am and the east-west axis of the market street, almost at the center of the fort. Its arrangement is that of an imperial mosque, after the Friday mosque at Ajmer built by Shah Jahan from 1637-38, and its layout is comparable that of the audience hall in the Agra Fort's Diwan-i 'Am. The arrangement of arches along the eastern elevation of the prayer hall was unusual for a mosque, which generally featured a taller, grander central portal, the better to emphasize the axis leading to the mihrab. The Moti mosque does not follow this pattern, and its scale places it between a private and a congregational mosque.

Built on a high plinth occupying ground that slopes towards the east, the mosque is oriented east-west, along the slope, and faces the Yamuna River. Its perimeter defines a rectangular space measuring 71.4 meters east-west and 57.2 meters north-south. It is composed of two parts: a nearly square courtyard with arcades along three sides and measuring approx. 47 meters per side precedes a covered prayer hall that runs along the western side.

The perimeter wall of the mosque is a blind wall clad with red sandstone on the outside and white marble within. Its outward-facing elevation is articulated with carved panels and simple relief work. The main entrance into the mosque is from a tall gateway structure in the centre of the eastern wall. Smaller gateways lead into the courtyard from the center of the north and south walls.
These gateways have ogee-arched entrances framed in arched iwans set into shallow rectangular frames. Three slender square pavilions with domed roofs crown each gateway. Stairways on either side of the entrance, running parallel to the courtyard arcades, access the roof.

The main entrance is through the larger eastern gateway, which is approached from the outside by two staircases rising along the red sandstone wall to culminate in a broad platform. The western surface of the gateway is articulated similarly to the other gateway structures, with an offset arched entrance crowned by square pavilions. Like the perimeter wall, each of the gateways is clad in red sandstone on the exterior and with white marble on the courtyard elevations.

An ablution tank measuring 11.35 meters per side is centered in the courtyard, which is wrapped with covered arcades on the north, south, and east. These arcades are 3.28 meters deep, with a roof supported every two meters by twelve-sided pillars. Cusped arches span between the pillars; above them runs a projecting eave (chhajja) around the courtyard, interrupted only by the gateway structures and the prayer hall. A solid parapet rises above the chhajja.

The prayer hall along the western edge of the courtyard measures 48.46 meters north-south direction and 17 meters east-west. A grid of massive pilasters organizes the interior space of the prayer hall into a series of seven equal bays north-south and three aisles running east-west. The central aisle is the widest, while the peripheral aisles are equal in width. The pilasters support cusped arches spanning in both directions, giving a repetitive rhythm to the aisles as well as the bays. The eastern (courtyard) elevation of the mosque reflects the bay division of the building as seven equal cusped arches set into shallow rectangular niches.

Above these arches run a frieze with a Persian inscription in black marble praising Shah Jahan and the mosque; this frieze is followed by a projecting stone eave. The horizontal line of the eave is followed by that of the blank parapet, and then surmounted by seven slender square pavilions that are aligned vertically with the arches of the eastern elevation.

Three bulbous domes, clad in white marble, rest on high drums atop the prayer hall. These are double domes; the exterior domes are onion-shaped and crowned with lotus finials, and the central dome is slightly larger than the others. Octagonal pavilions supported on slender columns and topped by domed roofs emphasize the four corners of the prayer hall.

The inside of the mosque has very little ornamentation: it is completely clad in white marble, with shallow relief work along the bases and capitals of the large columns. Within the prayer hall, the multi-lobed arches spanning between the large pilasters are pronounced with delicately offset sunken relief lines. Along the western (qibla) wall is a beautifully carved and inlaid mihrab flanked on either side by three shallow arched niches corresponding to the aisles. Every other bay in the center aisle has vaulted ceilings, corresponding to the roof domes. The remaining bays have a flat ceiling spanned by horizontal beams.

The prayer hall is flanked on either side by two relatively dark chambers, similar in width to the courtyard arcades. These chambers may have been designated for women's prayers; they are visually connected to the hall through fine stone jali screens, which allow the inhabitants to see the activity in the main hall while remaining unobserved. The arcades on either side of the prayer hall lead into these chambers and to staircases to the roof, located near the eastern elevation of the prayer hall.

The dominant material of the mosque is white marble, which covers every surface in the interior of the mosque; in contrast, the exterior walls of the mosque are clad in red sandstone and articulated with shallow blind arches topped with floral crenellations. The courtyard and the prayer hall are very simple: most of the surfaces are smooth, and the only articulation occurs in the joints between the different pieces of marble cladding a surface. The material continuity contributes to a spatial flow from the courtyard into the prayer hall.
The Moti mosque displays an austerity in its surface ornamentation, but one which serves to keep the focus on the beauty of its white marble cladding.

Sources:

Alfieri, Bianca Maria. Islamic Architecture of the Indian Subcontinent. London: Calmann and King Ltd., 2000. 242-245.

Koch, Ebba. "Diwan-I 'Amm and Chhil Sutun: The Audience Halls of Shah Jahan." Muqarnas 11, (1994): 143-165.

Nath, Ram. Agra and its Monuments. Agra: Historical Research Documentation Programme, 1997. 58-63.

Peck, Lucy. Agra: The Architectural Heritage. New Delhi: Lotus Collection, 2008. 62.