The Atlantic slave trade was the most famous example of a triangular trade system. European goods such as copper, cloth and guns were traded in African markets for African slaves, who were sent to the Americas and traded for raw materials such as sugar, rum and tobacco that were sent back to Europe. Historians refer to the transport of slaves across the Atlantic Ocean as the Middle Passage because it was the middle leg of the trade.

The living conditions on the ships that carried millions of African men, women and children across the water were extremely poor. On average each ship carried 400 slaves, who were shackled—often to one another—and made to stay in spaces below deck that were less than five feet high, packed so closely together that one observer said they looked “like books on a shelf…so close that the shelf would not easily contain one more.

As a result, disease was prevalent. There were breakouts of smallpox and yellow fever, and other illnesses such as dysentery were very common. Those who didn’t perish outright from sickness ran the risk of being thrown overboard to prevent further spread of the disease.

Many more chose to jump overboard; they considered drowning preferable to the voyage’s harsh, agonizing and unpredictable conditions, and the uncertain future that lay ahead. Others mounted failed insurrections against those who held them in bondage, and were put to death. It is estimated that ten to fifteen percent of the Africans brought over on these ships perished.

In his autobiography The Interesting Narrative of the Life of Olaudah Equiano, the former slave Equiano writes of his journey on the Middle Passage: “Often did I think many of the inhabitants of the deep much happier than myself.” In Gem of the Ocean, those inhabitants of the deep have built the City of Bones, an underwater kingdom where they continue to live, not merely rest in peace.