"Rock Island Line" is an American folk song that started as a spiritual sung by enslaved people in the Mississippi River Valley. It tells the story of a train operator who cleverly smuggles pig iron past a toll gate by claiming his cargo is merely livestock. The song was first recorded in prisons of the American South by folklorist John Lomax, who sought to preserve these spirituals before they were lost. Lead Belly later recorded a narrative version that became widely influential. Johnny Cash, known for his deep voice and songs often exploring themes of sorrow and redemption, brings his distinctive train-like rhythm to this tale of wit and defiance.