Hippocrates was an ancient Greek physician born around 430 BC who is considered the father of modern medicine. He rejected superstition in favor of scientific observation and created standards for physicians. Hippocrates founded a medical school on the island of Cos and traveled throughout Greece practicing medicine. He authored around 70 medical works that comprised the Hippocratic Corpus, establishing medicine as a science based on theory and observation. Hippocrates studied anatomy, physiology and the causes of disease, believing illness was caused by imbalances of the four humors in the body. He is renowned for establishing high ethical standards through the Hippocratic Oath and writings on environmental influences, exercise and hygiene.