It is believed to have been found by an African slave on the coast of the isle of Santa Margarita in the Gulf of Panama in the mid-16th Century or as early as the 15th Century.

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T-shirt, Mr Gates is as much a character in the television films as the characters he discusses: King Solomon or Don Francisco de Souza, Ivory Coast's most notorious slave trader.

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Cape Coast Castle was the grandest of the slave emporiums, at the centre of the trade.

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But in present-day Ghana, then called the Gold Coast, there were over 30 more slave forts, built and maintained by almost all of the European trading powers of the day: the Swedes, Danes, French, British, Dutch and Portuguese.

ECONOMIST: Slavery