Scandalous Error provides the first comprehensive study on the history of calendar reform and calendrical astronomy in medieval Europe. It covers a period of more than 1600 years, from the introduction of the Julian calendar in 46/45 BC to the Gregorian calendar reform of 1582, and draws on a broad range of sources, many of them previously unknown or unpublished, in an effort to shed substantial new light on the place of astronomy in medieval intellectual culture.