After the fall of the Western Roman Empire, the Byzantines and Arabs became the bearers of ancient medical knowledge and contributed to it. What little was preserved in Europe was kept in monasteries. Christianity played a large role, although a dual one, in the development of medicine. According to religion, the development of medicine in Europe is divided into monastic and scholastic medicine. Many medical schools are opened under the supervision of the Church. The exception was the school in Salerno, which acted independently. The Church and Christianity have also played a big role in people's attitude towards illness, so illness is often seen as a punishment for sin. In order to explain the occurrence of diseases, numerous theories were created, such as the miasmatic theory and the theory of the four bodily humors. Disease prevention was extremely important, so proper nutrition, exercise and fresh air were advised. The diagnosis of the disease was complicated, and included blood, urine, stool, and pulse tests. In the treatment, numbers of grasses, minerals, relics, amulets, teriacs were used. Often without effect. Epidemics were the most devastating for the medieval population, especially the two great plague epidemics that claimed around twenty-five million lives in Europe.