Perhaps because of the devastation caused by the disease, healers and physicians focused attention on it and its prevention. The first step in prevention and treatment is understanding the nature of the disease. The first physician to differentiate between smallpox and measles, which may seem similar at the outset, was Abu Bakr Muhammad Ibn Zakariya al-Razi (?850-923) or Rhazes, as he was called in the Latin West. In his De variolis et morbillis commentarius he makes the distinction.