Anthony Giacchino thumbed through a stack of letters, all of them marked with yellow stickers, red stamps or a simple, final X slashed through the addressee’s names: Clotilde Terranova. Rosie Friedman. Rosaria, Lucia and Catherine Maltese. “Return to sender,” he said. “Return. Return. Return. It’s like, ‘Who is this person?’ They’re forgotten, and unfortunately there’s a lot of truth to that.”

Dead letters? Not to Mr. Giacchino, who thinks of them more as correspondence with another century, addressed to the 146 victims of the Triangle shirtwaist factory fire.

As New York prepares to mark the centennial of the tragedy on March 25, he has mailed the letters to the places where each victim lived in 1911, as part of an art project to commemorate the workers and their place in the city. He is also reclaiming a part of Italian-American history — 39 Italian workers were among the dead — that has gone unexplored....