I looked upon the Nile and raised the pyramids above it. (7)
The pyramids are one of the seven wonders of the world. Whenever we see a picture of them, we immediately known what they are – they are that embedded in our imagination and in our memories. When we think back to ancient Egypt, perhaps we think about people like Cleopatra, King Tut, or other famous royal people. In this line, however, we hear the unique perspective of a peasant, of someone who actually helped to build the pyramids (rather than order them to be built). We get a different historical perspective.
I heard the singing of the Mississippi when Abe Lincoln went down to New Orleans, and I’ve seen its muddy bosom turn all golden in the sunset. (8-10)
Here, our speaker invokes a corner of history that we don’t always read about. We know Abe Lincoln delivered the Emancipation Proclamation and successfully abolished slavery during his presidential term. In this line, we are reminded of how powerful memory is, and how events can seem more magical in our remembering of it than perhaps they really are. Our speaker’s memory involves a river that sings and that transforms into gold. The poem has a magical, mystical quality in this way.