Probably the single most significant event in the emergence of philosophical debate was the foundation of universities such as those of Paris and Oxford. Of them all, Paris was the most international and vital. The principal centers of learning were founded by papal or imperial charter and date from the thirteenth century CE. Being independent corporations with licenses to grant degrees they could be relatively free arenas for intellectual debate. So the great age of medieval philosophy was from the thirteenth century onwards. It may also be noted that times were propitious for the revival of learning. Intercourse between Muslims, Jews and Christians in Spain helped to promote the translation of works of such notable figures as ibn Rushd and ibn Sīnā (Averroes and Avicenna), and also classical works. This could permit, for instance, the resuscitation of Aristotelian ways of thinking, especially under the stimulus of the new synthesis produced by Thomas Aquinas. Prior to this great period, there was, too, in the twelfth century what might be described as the ‘pre-university’ of Paris, in that the Parisian schools were already attracting attention and scholars.