known rivers

I looked out the window of the Pullman at the great muddy river flowing down toward the heart of the South, and I began to think what that river, the old Mississippi, had meant to Negroes in the past—how to be sold down the river was the worst fate that could overtake a slave in times of bondage. Then I remembered reading how Abraham Lincoln had made a trip down the Mississippi on a raft to New Orleans, and how he had seen slavery at its worst, and had decided within himself that it should be removed from American life. Then I began to think about other rivers in our past—the Congo, and the Niger, and the Nile in Africa—and the thought came to me: “I’ve known rivers,” and I put it down on the back of an envelope I had in my pocket, and within the space of ten or fifteen minutes, as the train gathered speed in the dusk, I had written the poem, which I called “The Negro Speaks of Rivers.”

—Langston Hughes, The Big Sea, in The Langston Hughes Reader (G. Braziller, 1958).