Symbolism is such an important aspect of this novel, and symbols such as fog, darkness and the river are crucial to understanding the novel and how Conrad builds up his picture of Africa during the era of Imperialism. The river is a key symbol throughout the novel, and in particular, towards the beginning, Marlow describes how as a child it had captivated him. He talks about the time he spent poring over maps and dreaming about travelling:
But there was in it one river especially, a mighty big river, that you could see on the map, resembling an immense snake uncoiled, with its head in the sea, its body at rest curving afar over a vast country, and its tail lost in the depths of the land. As I looked at the map of it in a shop-window, it fascinated me as a snake would a bird--a silly little bird!
Note the simile that compares Marlow to a bird being captivated and charmed by the snake-like river. Marlow from the first associates the river leading to the "heart of darkness" with temptation and evil. The symbol of the river is expanded when its value to Europeans is considered. It gives them access to the centre of Africa without having to laboriously trek through the land, meaning Europeans can travel swiftly and that Africa itself is only depicted through flashes as the boat moves down the coast and up the river. It is a symbol therefore of separateness, as it allows Europeans to venture into Africa without ever having to be part of Africa. In addition, the river itself seems to be a symbol of the way that Africa tries to shun or discourage Europeans from venturing on their soil: the current makes it difficult to go upstream, but the speed of the current seems to represent Africa itself trying to wash out or get rid of the European interlopers that walk on her land. The river therefore is one important symbol that reveals a lot about Conrad's depiction of Imperialism and Africa and white man's part in it.