The history of Kilwa is known from the Kilwa Chronicle which relates the history of the city from its foundation to the beginning of the Portuguese period in the sixteenth century. The earliest settlement at the site seems to have been in the eighth century although there are few standing remains from this period. At some time between the ninth and the twelfth century the settlement was taken over by a new dynasty from Shiraz in Iran who established themselves as sultans of Kilwa. The first sultan was Ali bin al-Hasan who is said to have bought the town from a pagan. The sultans of Kilwa continued to rule the town until the nineteenth century when the last sultan was deported to Zanzibar.

The wealth of the town depended on trade in ivory and other goods, but the most important commodity was gold. Gold was mined in the area of the African city of Great Zimbabwe and taken to the coast at Sofala (present-day Beira), from which it was shipped up the coast via Kilwa. There was also an overland route from Kilwa to Lake Nyasa and the Zambezi but this was always secondary to the sea routes. Sometime in the thirteenth century the sultans of Kilwa seem to have gained direct control of Sofala.

The wealth brought in by the gold trade meant that Kilwa had its own mint and was the only place in sub-Saharan Africa to issue coins. In 1332 the city was visited by Ibn Battuta who decribed it as one of the most beautiful and best-constructed towns he had visited. The wealth of Kilwa was legendary and it was mentioned by Milton in 'Paradise Lost' where it is called 'Quiloa'. However, the arrival of the Portuguese at the beginning of the sixteenth century brought an abrupt end to the prosperity of the city. During the seventeenth century the city seemed to have declined, and to have become a very small settlement, and it was only with the establishment of an Omani base there in the eighteenth century that the city again rose to prosperity. By the nineteenth century the city had again declined to a point where the administrative centre was moved to the mainland settlement of Kilwa Kivinje. The history of the city is reflected in the surviving buildings, although it should be remembered that the number of stone buildings was small compared to a majority made out of less permanent materials. The main building materials on the island were the same as elsewhere on the coast and included reef and fossil coral used as stone, mangrove poles for wood and coconut palms for roofing. A notable feature of the medieval architecture of Kilwa is the use of domes which is not paralleled anywhere else on the East African coast at this early period. With the exception of some domes in the palace of Husuni Kubwa all of the domes in the Kilwa area are supported on squinches. Elsewhere on Kilwa buildings are covered either with barrel vaults or flat roofs made out of wood and concrete. The Makutani Palace may be an exception to this as it seems to have had a wooden roof covered with palm thatch (makuti).

The main buildings on Kilwa are the Great Mosque and the Great House, the Small Domed Mosque, the Jangwam Mosque, the palace of Husuni Kubwa and the nearby Husuni Ndogo, the Makutani palace and the Gereza fort. There are also important ruins on nearby islands including Songo Mnara, Sanje Majoma and Sanje ya Kate.

The best-known building in Kilwa is the Great Mosque which is a large complex structure dating from several periods. The building consists of two main parts, a small northern part divided into sixteen bays and a larger southern extension divided into thirty bays. The earliest phase evident at the mosque is dated to the tenth century although little survives of this above foundation level. The earliest standing area of the mosque is the northern part which dates to the eleventh or tenth century and was modified at the beginning of the thirteenth. This area was probably covered with a flat roof supported on nine timber columns. The next phase included the addition of a large cloistered courtyard to the south supported on monolithic coral stone columns and a small chamber to the south-west covered by a large dome. This was probably the sultan's personal prayer room and the dome is the largest dome on the East African coast, with a diameter of nearly 5 m. Also belonging to this period is the southern ablutions courtyard which included a well, latrines and at least three water tanks. Sometime in the fifteenth century this arcaded southern courtyard was rebuilt and covered over with the present arrangement of domes and barrel vaults supported on composite octagonal columns, making this the largest pre-nineteenth-century mosque in East Africa.

Adjacent to the Great Mosque on the south side is the Great House which mostly dates to the same period as the latest phase of the mosque (i.e. eighteenth century). The Great House actually consists of three connected residential units each with a sunken central courtyard. Most of the complex would have been a single storey although a second floor was added to some of the central area. The purpose of the Great House is not known, but it is likely that at some stage it served as the sultan's residence judging from a royal tombstone found during excavations.

To the south-west of the Great Mosque is the Small Domed Mosque which together with the Jangwani Mosque are the only two examples of a nine-domed mosque in this area. This building probably dates from the mid-fifteenth century (it is built on an earlier structure) and contains an arrangement of vaults and domes similar to the later phase of the Great Mosque. There are only two entrances, one on the south side opposite the mihrab and one in the centre of the east side. Domes cover most of the area of the mosque except for two bays covered with barrel vaults, one next to the entrance and one in front of the mihrab. The central bays are differentiated from the side bays by being wider and by the use of barrel vaults at either end, emphasizing the north-south axis. The dominant feature of the mosque is the central dome which is crowned with an octagonal pillar and internally contains three concentric circles of Islamic glazed bowls set within the dome. The two vaults to the north and south of the central dome are also decorated with inset bowls of glazed ceramics whilst the two domes either side of it are fluted internally; the other four domes are plain internally.

The other nine-domed mosque is of approximately the same date and is known as the Jangwani Mosque; it is located to the south of the Small Domed Mosque. Although more ruinous, excavation has shown this mosque to be similar, with the same use of fluted and plain domes, and entrances only on the south and east sides.

To the east of the main group of buildings are the remains known as Husuni Kubwa (large Husuni) and Husuni Ndogo (small Husuni). The term Husuni derives from the Arabic term husn meaning fortified enclosure or fortress. Whilst this term may be appropriate for the the latter, its application to Husuni Kubwa seems unlikely for a palace complex. Husuni Kubwa is located on a coastal headland overlooking the Indian Ocean. It seems to date mostly from the late thirteenth or early fourteenth century and may well have never been completed. The complex consists of three main elements, the gateway or monumental entrance, the large south court and a complex of four courtyards which form the core of the palace. Also at the northern end of the complex there is a separate private mosque located on rocks next to the sea and reached by a staircase. The four courtyards at the northern end of the complex comprise an audience court, a domestic court, a bathing pool and a palace court. On the east side of the audience court are a flight of steps leading up to a flat-roofed pavilion which has been interpreted as the sultan's throne room. To the east of this is the domestic court which opens on to a complex of residential rooms, or beyts. The bathing pool consists of a sunken octagonal structure with steps and lobed recesses on each side. The palace court at the northern end of the palace is a sunken rectangular structure aligned north-south with steps at either end. The north set of steps leads to a further residential unit which overlooks the sea and the small mosque. It is possible that the sea mosque and the staircase represent the sultan's private entry to the palace. The royal nature of the palace is confirmed by a floriated Kufic inscription found during excavations which mentioned Sultan al-Hasn bin Sulayman.

By contrast Husuni Kubwa is a severe-looking building which fits the name Husuni (fort). It consists of a rectangular structure aligned north-south and measuring over 70 m long by more than 50 m wide. Thirteen evenly spaced, solid, semi-circular bastions protect the outside of the wall with one rectangular tower on the west side. The only entrance is in the middle of the south side and consists of a wide gateway leading into a gateway with the exit on the east side thus forming a bent entrance. Excavations have revealed the traces of a few structures inside but these may be later and do not give any indication of the function of the building which is unparalleled elsewhere in East Africa and suggests an outside influence. There is little evidence for dating this structure although it is thought to be contemporary with Husuni Kubwa.

The other two important buildings on Kilwa island are also defensive structures although they seem to date mostly to the eighteenth century. The largest of these is the Makutani palace which was the residence of the sultan in the eighteenth century. This building is contained within a fortified enclosure known as the Makutani, which consists of two curtain walls fortified by square towers with embrasures. The wall was originally approximately 3 m high and crenellated. Although there is no trace of a parapet this could have been built of wood like many other features of the eighteenth-century remains at Kilwa. The palace occupies a position between the two enclosure walls and appears to be built around one of the earlier towers. It is the only building on the island still to have an upper floor which contained the main residential area of the palace.

The Gereza or fort is located between the Makutani palace and the Great Mosque. It consists of a roughly square enclosure with two towers at opposite corners. Although there is some evidence that the original structure was Portuguese, the present form of the building seems to be typical of Omani forts.

In addition to sites on Kilwa island there are important sites on nearby islands. The earliest of these sites is Sanje ya Kate, an island to the south of Kilwa where there are ruins covering an area of 400 acres, including houses and a mosque. The mosque is of an early type with a mihrab niche contained in the thickness of the wall rather than projecting out of the north wall as is usual in later East African mosques. Excavations have shown that the settlement was abandoned before 1200 and most of the ruins date to the tenth century or even earlier.

To the east of Sanje ya Kate is the larger island of Songo Mnara which contains extensive ruins on its northern tip. The remains date to the fourteenth and fifteenth centuries and consist of thirty-three houses and a palace complex, as well as five mosques contained within a defensive enclosure wall. The remains at Songo Mnara are informative as they are one of the few places in East Africa where pre-eighteenth-century houses survive in any numbers. The houses have a standardized design with a monumental entrance approached by a flight of steps leading via an anteroom into a sunken courtyard, to the south of which are the main living quarters of the house. [hide description]