Were the Swahili stone towns Arab colonies or African cities?

Were the stone towns of East Africa Arab colonies, or African cities? The evidence points to a both-and answer: the towns grew from African communities, got rich on an ocean-wide trade, and their culture formed from a mix of African and Arab origins.

The coast in question is the Indian Ocean shore of East Africa, including islands such as Zanzibar and the Comoros. Bantu farmers are considered its initial settlers and built communities along the coast, and those coastal communities shared archaeological and linguistic features with the interior of the continent. The Swahili people and culture formed from a distinct mix of African and Arab origins; the word Swahili itself comes from Arabic for coasts. The language is Bantu, with heavy Arabic influence.

The key was the monsoon. Yearly winds carried ships from the Swahili coast to the eastern Indian Ocean and back, and made the trip predictable. The coast exported timber, ivory, animal skins, spices and gold, and imported silk and porcelain from China, spices and cotton from India, and black pepper from Sri Lanka. Archaeologists trace it through pot shards found at coastal sites that trace back to China and India.

At the centre of all this stood towns such as Kilwa, a city that Ibn Battuta called one of the most beautiful in the world. Kilwa levied a customs duty on gold shipped north from Zimbabwe. Its sultans built in stone, including Kilwa's fortress and palaces. The Swahili coast was essentially an urban civilization revolving around trade, and some estimate that its towns minted coins from the 9th century.