Al-Ghazali (1058-1111) wrote the Revival of the Religious Sciences (Ihya' ulum al-din), joining knowledge, worship and the purification of the heart. Ibn Rushd (1126-1198), judge and philosopher of Cordoba, wrote commentaries on Aristotle and a book comparing the juristic opinions of the schools, Bidayat al-Mujtahid. Ibn Khaldun (1332-1406) wrote the Muqaddima in 1377, an introduction to history that studies the rise and fall of societies, economy and education. Knowledge also travelled: after Toledo came under Christian rule in 1085, scholars such as Gerard of Cremona translated Arabic books, including the Canon of Medicine, into Latin. Scholars did not agree on everything and debated each other strongly, and the idea of a single 'golden age' is a simplification: learning continued in many regions and centuries. The lesson for today is the habit of serious study, open debate within the limits of faith and good manners, and service to people.