"As the dynamics of trade relations began to change during the African Middle Ages, the continent became the source of endless speculation. The visions of monstrous men and anthropophagi that had filled St. Augustine's descriptions of sub-Saharan Africa were not expelled until other Europeans such as Scotsman Mungo Park "penetrated the interior of Africa." In the European tradition "blackness," an extension of Africa, is often thought of as a resistant force, racially charged matter that must be penetrated-thus the descent into darkness. In 1899 Joseph Conrad published The Heart of Darkness, a work that has inspired perhaps more sf stories (and criticism) than any other work of fiction. Premier genre critic John Clute writes that this twentieth-century classic's "grueling odyssey into the unknown, and its vision of the Otherness of alien life, has captured the imagination of sf writers ever since." In this description the "unknown" element alluded to is the African continent or, more specifically, the Belgian Congo of 1890; and "the Otherness of alien life" is the Africans themselves."