The hourglass is one of the most recognizable instruments ever devised for measuring the passage of time, yet its origins are far more mysterious than those of the sundial or the water clock. Unlike those earlier devices, whose histories can be traced back to ancient Egypt, Mesopotamia, Greece, and China, the hourglass appears relatively late in the historical record. Despite frequent claims that the Romans or ancient Greeks invented it, no convincing archaeological or written evidence supports those assertions. Historians generally agree that the hourglass emerged in medieval Europe sometime between the eighth and fourteenth centuries,
