Muhammad al-Idrisi produced in 1154, commissioned by Roger II of Sicily, one of the most ambitious geographic and cartographic works of the Middle Ages. After fifteen years of work integrating Arabic sources, merchants' accounts, and the Greek tradition, he produced a world map richer and more accurate than any contemporary European chart. That his work was produced at a multicultural Norman court — Arab, Greek, Latin — makes al-Idrisi an especially clear case of Islamic knowledge entering Europe without receiving due credit.