Why does Langston Hughes repeat the line, "I've known rivers," in the Poetry "The Negro Speaks of Rivers."

Answer 1

http://www.google.com/search?q=rivers+africa+america&ie=utf-8&oe=utf-8&aq=t&client=firefox-a&rlz=1R1GGGL_en___US357

Think of those who were captured and enslaved in Africa. Where did most of them live? Then think of their journey across the sea. Then think of their life on the plantations.

What rivers???