It all started on a former plantation in Tennessee. That's where Sandra Arnold's great-grandfather, Ben Harmon, who was born a slave, is buried next to his wife, Ethel. Their final resting spots are clearly marked, gravestone and all, but next to them, Arnold noticed an entire area of unmarked slave graves. She wondered if they could be family, too.
Her research started on that plot, then expanded to the state of Tennessee. Eventually, Arnold learned that it wasn't uncommon to find unmarked slave burial places across the country.