Henry Louis Gates Jr. is the Alphonse Fletcher University Professor and the director of the W.E.B. Du Bois Institute for African and African-American Research at Harvard University. He is also the editor-in-chief of The Root. Follow him on Twitter and Facebook.

In last week's column on the Colfax Massacre of 1873, I closed with a reference to Barack Obama's July 19 discussion of Trayvon Martin and the "set of experiences and a history that doesn't go away." Speaking from the White House as president and as a man from within that veil of "experiences," he explained, "There are very few African Americans who haven't had the experience of getting on an elevator and a woman clutching her purse nervously and holding her breath until she had a chance to get off. That happens often."

It does happen often, and I imagine it always has ever since the first commercial elevator was installed in Manhattan by the Otis Elevator Company in March 1857 (just two weeks after the U.S. Supreme Court handed down the Dred Scott decision casting blacks out of citizenship and the meaning of "We, the people"). And it continued happening whenever black people were allowed to ride as passengers (rather than as operators) in elevators -- that rush to the elevator doors -- even though, contrary to the stereotype, it was a black man, the brilliant inventor Alexander Miles of Duluth, Minn., who patented a way for those doors to open and close automatically in 1887. That same year, Florida passed the first state law requiring segregation in public accommodations, and for much of the Jim Crow era that followed, Congress, hemmed in by the Supreme Court, was unwilling to do anything to protect blacks' civil rights, not even passing an anti-lynching bill.

So however many white purses were clutched, or breaths held, when a black man entered a public elevator, he was among the most vulnerable passengers anywhere in the United States. This is the story of one such rider who, without any eyewitnesses, became the flashpoint for one of the deadliest race riots in American history....