The primary use of symbolism in this poem is the symbolism of the rivers. The speaker, who represents African Americans, connects his history, and thus the history of African Americans, to the eponymous rivers. This history, which the speaker also equates with the African American "soul," is "deep" and "ancient," like the rivers.
Different rivers referenced in the poem have different, specific symbolic meanings. The Euphrates, for example, was a river running near to Mesopotamia, an area often considered to be the birthplace of civilization. In the poem, therefore, the Euphrates symbolizes the idea that African American history has deep, ancient roots.
The Nile river was vital to Ancient Egypt because Egyptians were able to use the moist land close to the Nile to grow crops. The Nile River is thus symbolically important as a source of life. The pyramids which the poet refers to in the same line are also important as symbols of slavery. Indeed, the pyramids were built by slaves. The Mississippi river also has symbolic links to slavery. There were approximately 437,000 slaves in the state of Mississippi by 1860. The history of slavery, in Africa and latterly America, is of course of huge significance to African American history.
When the speaker refers to "the Euphrates," he also, in the same line, refers to a time "when dawns were young." Toward the end of the poem, the speaker refers to the "bosom" of the Mississippi river turning "golden in the sunset." The "dawns" and the "sunset" are also used symbolically in the poem, with the former being used to symbolize the beginning of African American history and the latter perhaps being used to symbolize the ending of a period of that same history.