The Great Mosque of Kilwa is the earliest remaining mosque structure on the East African coast, though it is predated by elements from the Kizimkazi Mosque in Zanzibar. The Great Mosque, which now stands at the edge of modern Kilwa, was built in at least two distinct stages, which can be seen in the marked difference between the small northern prayer hall built in the eleventh and twelfth centuries and the subsequent fourteenth century southern enlargement. Furthermore, segments of a tenth century foundation predate both sections of the existing mosque layout. The Great Mosque of Kilwa, which is entirely roofed by domes and vaults, has since its construction been widely acknowledged as one of the first mosques built without a courtyard.
Northern Prayer Hall The original prayer hall was built in the eleventh or twelfth century and was subsequently modified in the thirteenth century. It was composed of 16 bays divided by nine pillars holding a flat roof of coral plaster. The original pillars were octagonal columns each carved from a single coral stone and measuring 140 centimeters tall and 40 centimeters square. Coral stone has a lime content that hardens with water and saturates the porous coral to create concrete. This sanctuary measured about 7.8 meters side and 12 meters along the qibla axis. The east and western side wall each had three arched doors that were embellished in the thirteenth century with recessed spandrels.
With the thirteenth century modifications the columns were replaced with those made of timber and a more elaborate roof support structure, including transverse beams and side pilasters, was installed. According to the Kilwa Chronicle, the beams and columns were installed in wood because stone carving craftsmanship in Kilwa had declined. The coral blocks of the ceiling were also plastered with concrete upon which an interlocking circular pattern was engraved. The original walls of the mosque were lined with a second wall of square cut coral blocks set in a thick mortar.
The later mihrab in the northern prayer hall likely dates from the fifteenth century because of its stylistic elements. Its high arch, surrounded by a boldly framed architrave, is rebated by chamfered pilasters. The recessed apse has a fluted semi-dome and multiple string courses. To the east of this mihrab are four dressed blocks of coral stone projecting from the wall in a shelf and probably indicating a minbar.
Northern Ablution Area To the west of this prayer hall was an ablution court joined to the mosque via an anteroom. This sunken courtyard contained a tank, a well, and a washroom, as well as large round sandstone blocks set in the floor to exfoliate the feet after washing. From the south side of this court, a stairway leads to the roof. The northwest corner of the anteroom leads to a small vaulted chamber that may have served as a private room for the imam. From this room an unroofed passageway runs along the north exterior of the mosque behind the qibla wall. This passageway was partially divided and may have been used or intended for the placement of graves as was common in the coastal tradition.
Southern extension and the Great Dome In the early fourteenth century, Sultan al-Hasan ibn Sulaiman, the builder of the palace of Husuni Kubwa, built an extension from the east wall of the northern prayer hall, which wrapped around forming a large open court. A very narrow barrel vaulted corridor, consisting of 30 bays complete with dressed coral panels and supported by coral columns ran directly southward. This extension juts out slightly to the east, creating a wing that deviates from the otherwise orthogonal plan. Within the space where the wall splays, two small irregular rooms were preceded by a small porch containing a tank filled with smooth quartz pebbles, a sandstone foot-rubber and a bench. Behind this small assembly of rooms is a somewhat larger plainly vaulted room. This long room leads into a square room four meters across which carries the great dome.
This dome, noted in the Kilwa Chronicle, is thought to be the first true dome on Africa's east coast. It was supported on squinches and decorated with dressed coral panels. After his visit in 1331, Ibn Battuta remarked on the splendor of the dome, which was, until the nineteenth century, the largest dome on the East African coast. Beyond the Great Dome is a string of ablution rooms with a well. Latrines and water tanks were added, partially enclosing a large open space between it and the northern prayer hall.
Southern Enclosure According to the Kilwa Chronicle, after the death of ibn Sulaiman in 1333 the mosque fell into ruin. Not until the early fifteenth century, under the reign of Sultan Sulaiman ibn Muhammad, was the mosque reconstructed and the southern fully court enclosed. Sometime between 1421 and 1442, the southern hall was roofed with barrel vaults with domes placed atop alternate bays. This extension made the Great Mosque at Kilwa the largest covered mosque on the east coast of Africa.
The southern enclosure utilized the pre-extant enclosure walls to the north, south and east and created a new 20 meters long western wall which squared off the space. The enclosure was then divided into 30 bays, six aisles long and five aisles wide from east to west. The bays lining the perimeter of the enclosure as well as the bays in the central north-south aisle are surmounted by domes, the most northern and southern of which were shallower than the rest. The two domes serving as entrance bays along the eastern side are internally fluted. The more southern of these fluted domes enters from the great dome. The remaining eight bays, which flank the central axis, are barrel vaulted. Due to the slightly irregular angles of the southern court a few of the bays are shortened by 20 centimeters.
As with the other vaults from Kilwa, the Great Mosque's vaults and domes are constructed out of lime coral concrete. These domes are about 20 to 30 centimeters thick and shaped into hemispheres supported by groined squinches between which run pointed arches. These arches are supported by two-tiered columns which are octagonal at their base and become squared half way up. The octagonal segments of the columns have rectangular coral panels on the alternating faces. Along the walls the arches are supported by engaged columns or corbelled brackets. The capitals of the columns were made from single coral blocks and carved with concave carved angle brackets. On the western face of the enclosure, windows and doors alternate in the bays between the embedded columns.
A large room with a corbelled roof was built at the far southwest corner of the southern hall. Two doors lead from the south wall onto a narrow lane separating the Great Mosque from the Great House complex.
A final addition of a second mihrab was added at a much later date. The mihrab for the larger congregation using the south hall is located at the northernmost end of the central axis and juts into the northern prayer hall.
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Chittick, Neville. 1974. Kilwa: An Islamic Trading City on the East African Coast, vol 2. Nairobi: British Institute in Eastern Africa, 61-66.
Garlake, Peter S. 1966. The Early Islamic Architecture of the East African Coast. London: Oxford University Press, 15, 17, 24, 35-36, 50, 51, 59, 61, 76-77, 84, 115.
Garlake, Peter. 2002. Early Art and Architecture of Africa. Oxford: Oxford University Press, 178-179.