Those that were most concerned with health, sanitation and illness in the ancient world were those in the elite class. Good health was thought to reduce the risk of spiritual defilement and therefore enhanced the social status of the ruling class who saw themselves as the beacon of civilization. During the late Roman Period, sanitation for the lower classes was a concern for the leisured class. Those that had the means would donate to charities that focused on the health of non-elites. After the decline of the Roman Empire, physicians and concern with public health disappeared except in the largest cities. Health and public doctors remained in the Byzantine Empire. Focusing on preventing the spread of diseases such as small pox lead to a smaller mortality rate in much of the western world. Other factors that allowed the modern rise in population include: better nutrition and environmental reforms (such as getting clean water supplies).