Harvard professor and author John Stauffer is considered an authority on Lincoln and the Civil War.
His latest book charts the evolution of the wartime ballad "Battle Hymn of the Republic".
Stauffer discussed the origin of the tune Thursday at the Lincoln Presidential Museum. The museum is wrapping up its summer series of book discussions.
Ahead of Stauffer's lecture, Peter Gray asked what inspired him to research what he calls "the song that marches on":