The premise that East Africans had to pay to bring goods into Kilwa is historically inaccurate.
Kilwa Kisiwani (on Tanzania's coast) was a major Swahili city-state (12th–15th centuries) that thrived as a trade hub. It connected:
Kilwa's wealth came from facilitating trade, not restricting it. The decline came from Portuguese disruption (1500s), not internal barriers.
Sources: Archaeological evidence, Portuguese chronicles, Swahili oral histories, and Indian Ocean trade scholarship.