Barbary Slavemaster — Allan Aldiss

This novel is set in a time and place where harem women really were totally at the mercy of the rich men who owned them, and of the black eunuchs who supervised them. European women really were captured by the Corsairs and sold in the slave markets of the East. The Barbary States did have a reputation for treating Christian slaves unbelievably harshly, almost as animals, and there actually were slave breeding farms in the Ottoman Empire ... and although you won't find Marsa on the map, there are several places where it well could have been.

The story takes place during the long drawn out war between Britain and revolutionary and then Napoleonic France, which started in 1793 and only ended with the Battle of Waterloo twenty-two years later.