Heart of Darkness Symbols
The symbols and allusions in this work are numerous, and it is unlikely scholars would agree on all of them. Here are a few of the more prevalent ones, though even these are debatable. See the analysis sections for specific quotes regarding these images (where not provided).
The jungle could be interpreted as knowledge. Conrad often alludes to it containing mysteries and possessing hidden knowledge.
The Knitting Women
Possibly the knitting women represent two of the three Greek Fates (Clotho and Lachesis). The third Fate,(Atropos or death), might be represented by the Company itself, or the portal to the "heart of darkness" that the Company provides.
Maps and characters' fascination with them are common in adventure stories, especially ones set in England where most adventures deal with some kind of seafaring. Maps represent adventure, possibility, the call to quest.
The Cannibals / the Natives:
Perhaps these are not really symbols, but they are definite representations of "the other", a common theme in literature.
When Marlow studies the river he is to traverse, he likens it to an "immense snake uncoiled" that fascinates him "as a snake would a bird" (60). Serpents can represent the devil, clearly. Later in the story, Marlow throws his shoes "unto the devil-god of that river" (113). These passages provide good evidence that the river symbolizes evil or the devil.