The setting of the Congo for The Heart of Darkness is a dark, evil one, indeed. For, the history of the Belgian Congo is rife with crimes against humanity, most of which were perpetrated by King Leopold II. Slavery, murder, mutilation, starvation, and complete exploitation of the native peoples and the bounty of the country characterized the colonial rule under this heinous king. As a result, the setting of Conrad's novel conjures this dark environment of evil and terrible exploitation of both man and beast. It creates an ominous tone, something dark and sinister. The slow journey down the river into the depths of the dark rain forest becomes symbolic of the passage into the "horror" found within the depths of man's soul when he has given himself over to the exploitation of other men.
The dark river which Marlow travels and the shore which reveals little creates a metaphoric sense of evil and a sense of foreboding. Marlow himself uses the word "dark" frequently; for instance, he speaks of "the starred darkness" as a metaphor for the way that people are affected morally by the environment. The author, Joseph Conrad, generates mood with his setting by the use of language as a literary technique. One critic writes that Conrad's use of language, while presenting the physical place, also intimates "the effect of the exterior landscape upon the interior landscape in a carefully articulated polyphonic counterpoint." For example, in Chapter 3, Marlow narrates,
I looked around, and I don't know why, but I assure you that never, never before, did this land, this river, this jungle, the very arch of this blazing sky, appear to me so hopeless and so dark, so impenetrable to human thought, so pitiless to human weakness.