The first part, set on an island in central Africa among descendants of classical Greek civilization, was printed in 1789 but immediately suppressed by Cumberland. A passage describing society everywhere except on the utopian island as oligarchic and unjust was deemed by his lawyer to be potentially seditious; the novel was only published a decade later, and then in revised form. The second part, set in central Africa's Mountains of the Moon among descendants of followers of a fourth-century Christian heretic, is published here for the first time. Cumberland was a widely cultivated and deeply humane dilettante. A poet, painter, distinguished collector of prints and shells, and scientific inventor, he was passionately concerned with the reform of politics and society. He was also friends with some of the best authors and painters of his time, including William Blake, who encouraged Cumberland's ideals. Bentley describes the similarities between Blake's radical analysis of society and his early ideas on free love, sexuality, slavery, natural religion, and energy and the ideals Cumberland espouses in The Captive of the Castle of Sennaar. Bentley provides historical and geographical appendixes, textual and commentary notes, and a comparison of Cumberland's work to Simon Berington's The Memoirs of Signor Gaudentino di Lucca. Bentley's edition of The Captive of the Castle of Sennaar will be of interest to Blake scholars and to students and scholars of utopian literature and late eighteenth-century and Romantic literature and culture.