On a recent warm afternoon, a small park in the Hunts Point section of the Bronx was empty except for one visitor — a jazz trombonist named Johnnie Butler, sitting beneath a weeping willow, practicing “A Long Drink of the Blues.” Mr. Butler lives in the neighborhood, and this is his favorite spot to play. He’s often solo, since there’s not a lot of foot traffic around Joseph Rodman Drake Park, mostly trucks serving the heavy industry in the area. There aren’t even any benches, so Mr. Butler brings his own chair.

Though he didn’t realize it, Mr. Butler was not completely alone. Not far from him, four feet below, lay the remains of a number of African-American slaves from the 18th and 19th centuries.

“I had no idea,” said Mr. Butler, taking five and looking down at the grass. “Maybe that’s why I’m attracted to this spot.”