Science in the Medieval World: Book of the Categories of NationsDuring the Middle Ages, a thriving center for learning and research was Muslim Spain, where students gathered to consult Arabic manuscripts of earlier scientific works and study with famous teachers. One of these teachers was Sa'id al Andalusi, who in 1068 wrote Kitab Tabaqat al 'Umam, or "Book of the Categories of Nations," which recorded the contributions to science of all known nations. Today, it is one of few surviving medieval Spanish Muslim