Scaffolding in a niche of the Vatican Museums’ Round Hall conceal from view the work of restorers who are removing centuries of grime from the largest known bronze statue of the ancient world: the gilded Hercules Mastai Righetti. For more than 150 years, the four-meter-tall (13-foot-tall) figure of the half-human Roman god of strength has stood in that niche, barely garnering notice among other antiquities because of the dark coating it had acquired.