An inscribed stone slab unearthed at an Etruscan site in Tuscany is proving to contain one of the most difficult texts to decipher. It was believed that the sixth-century B.C. stela would shed light on the still-mysterious Etruscan language, but so far it remains a puzzle. “To be honest, I’m not yet sure what type of text was incised on the stela,” says Rex Wallace, professor of classics at the University of Massachusetts. Inscribed with vertical dots and at least 70 legible letters, the four-foot-tall and two-foot-wide slab had been buried for more than 2,500 years in the foundations of...