Rooted in the Mississippi Delta, the blues sprang from the spiritual music and field hollers of slaves, spinning a cultural thread that followed the great black migration from South to North.

Recalling the seminal years of the blues, convicts pick cotton at the Louisiana State Penitentiary in Angola. The cadence of singing field-workers shaped the blues’ musical structure.

— From "Traveling the Blues Highway," April 1999, National Geographic magazine