There is an increase of settlements along and close to the shores along the stretch of the Swahili coast from Mogadishu to Sofala in Mozambique including the Lamu, Zanzibar and Comoros archipelagos and the northern tip of Madagascar. The communities were making and using a new suite of ceramics called Early Tana Traditions/ Triangular Incised Ware ETT/TTW characterized by necked jars with incised decorations. These were widely distributed along the coast by 8th century. These ceramics were also found further into the hinterland, suggesting expanded trade and a broader east African ecosystem. These ceramics were quite similar to the Urewe and Kwale ceramics because they were regional traditions and not tied to a specific cultural group.
Even though the term Swahili, originating from Arab-speaking visitors, was only used towards the end of this period, most believe that this was the period of Swahili origins. A new way of life begun as boats became important, with the coastal people now moving along the coast to start new settlements and with the movement, a new economic endevours like production of iron, construction of boats, fishing nets, shell beads and pottery. New goods as a result of further interaction with foreign merchants from the Persian Gulf, India, Southeast Asia, Maldives and Indonesia started coming in, including glazed ceramics, glassware, copper alloy, metal jewellery and stone and glass beads.
Trade in captive people started taking place around the 9th century (Kusimba 2004) with people brought from the hinterland transported through Zanzibar and Pemba to the Middle East. The Zanj Revolt of 868 in the Gulf of Basra included people of eastern African origin.
The Zanj Revolt
The Zanj Revolt, a major uprising against the Abbasid Caliphate, took place from 869 to 883 AD (though some sources mention the revolt started in 868). The revolt occurred near Basra in present-day southern Iraq and was led by Ali ibn Muhammad, a man whose ancestry is debatable, with sources claiming he was either of Persian or Arabian descent. The Zanj, East Africans (including Abyssinians, collectively called the Zanj) who were enslaved and exported via the Indian Ocean slave trade, primarily worked draining salt marshes in the region. It grew to involve slaves and freemen, including both Eastern Africans and Arabs, from several regions of the Caliphate, and claimed tens of thousands of lives before it was fully defeated after almost 15 years.[1]
During this 400-year period, contact with Muslim traders influenced the region significantly and evidences of Islam can be traced to the mid-eighth century with a timber mosque found at Shanga, Lamu
content credit: The Swahili World (Stephanie Wynee-Jones, Adria LaViolette)
[1] https://en.wikipedia.org/wiki/Zanj_Rebellion