Light came out of this river since-you say Knights? Yes, but it is like a running blaze on a plain, like a flash of lightning in the clouds. We live in the flicker-may it lasts as long as the old earth keeps rolling! But darkness was here yesterday. (Conrad 9).
What Marlow is saying here is that man's lust for the unknown, for the darkness, is a trait that has been present for as long as the earth has been turning. It makes no difference whether it is Romans journeying the Thames, or Marlow on the Congo, or Willard on the Nung. The metaphorical darkness is always there at the epicenter of the journey, and it will be forever. Coppola takes notice of this, and makes this one of the more prominent themes in the movie as Conrad does in the book.
And so, the journey up the river is the most indispensable connection between Coppola and Conrad, Willard and Marlow. But within the journey the two characters respectively assume, there lie the differences in cinematic framing. The overall thematic structure remains the same, but obviously the main distinction is the river setting. Marlow finds himself upon the Congo River in the late 1800's during a time of vast European colonization in Africa. Meanwhile, Willard finds himself on the Nung River during the chaos of the Vietnam War. .
The people they meet and the experiences they deal with still resemble each other in structure, but Coppola took the liberty to adapt the characters to the setting of Apocalypse Now so that he could modernize "the horror". A good example of this is at the first outposts that each of the men had to stop at in order to continue their missions. This overall thought is the same, each character having to stop at stations and collect Company (in Willard's case Army) materials and, ultimately, relieve Kurtz of his post. Marlow was to collect ivory and Willard was to collect information. Both Marlow and Willard begin to realize what the moral implications of .