Kilwa Kisiwani

A few hundred metres off the coast of Tanzania there is a small island. On it stand a mosque with fallen domes, the ruin of a palace looking out to sea, and walls eaten by salt wind. The place is called Kilwa Kisiwani — Kilwa on the island.

The material of those walls is unusual: coral. Coral stone cut from the reef is soft when it comes out and can be shaped with a blade; it hardens as it meets the air. The city was quarried out of the sea in front of it.

A City-State On The Coast

Kilwa was one of the Swahili city-states strung along the East African coast. These towns did not belong to an empire; each ran its own harbour, its own ruler and its own trading network. What they shared was a language — Swahili — and a calendar set by the monsoon.

The monsoon is the engine of that trade. For part of the year the wind blows from the north-east and carries sailing ships from Arabia, Persia and India down to the African coast. Months later it reverses and takes the same ships back. That means waiting months between arrival and departure, and that wait turned the coastal towns into places to lodge and store.

From the eleventh century Kilwa became one of the wealthiest knots in the network. It minted its own money — excavated copper coins carry the names of the town's rulers.

The Gold It Never Saw

Kilwa's wealth did not come out of its own ground. The main earner was gold, and the gold was mined not on the island but far to the south and far inland, on the plateau of present-day Zimbabwe. From there it came down by caravan to the coast, to the port of Sofala.

What Kilwa did was not to work the mine but to control the line running to Sofala. A merchant arriving from the north had to pass through Kilwa's permission and Kilwa's ships to reach the gold. The town grew rich not by producing but by standing in between.

That detail connects directly to another monument in this register: at the place that gold came from, the stone walls of Great Zimbabwe were going up. The two never saw each other, but they were at opposite ends of the same trade.

Mosque, Palace, Bath

The first phase of the Great Mosque goes back to the eleventh century; over the next two hundred years it was enlarged and roofed with domes and vaults. When it was finished it was the largest mosque in sub-Saharan Africa.

Early in the fourteenth century, Sultan al-Hasan ibn Sulaiman built Husuni Kubwa on a headland outside the town: a terraced palace and warehouse complex of some hundred rooms looking over the sea, with an octagonal bathing pool inside it. The building was never completed and was abandoned soon after. Why is not known.

The Moroccan traveller Ibn Battuta, who called here in 1331, describes Kilwa as among the best-built towns he had seen.

Today

In 1505 a Portuguese fleet sacked the town and built a fort. The trade routes changed, Kilwa's role as an intermediary dissolved, and over the following centuries the town shrank and emptied.

The site was inscribed on the UNESCO World Heritage list in 1981 and sat on the danger list from 2004 to 2014. The threat here comes straight off the water: wave erosion is eating the shoreline, salt works into the coral stone and crumbles it, and rising sea level is pressing on the foundations of the quayside buildings. The material the city was made of came out of the water that is now consuming it.