Madrasas, in Islamic civilizations, were teaching institutions, some of which focussed on medicine. These madrasas were often closely linked with hospitals so that students could learn in the institutions and put their theoretical knowledge into practice in the hospitals. Physicians were not exclusively Muslim; practicing physicians included Jews, and Christians. In the major hospitals at Cairo, Baghdad, and Damascus, students could visit patients often with the supervision of a practicing physician, in a system that is comparable to that of medical residents today.