In many respects, the first six cholera pandemics served as prologue to the present. The disease spread rapidly on a path of human destruction that seemed as random as it was terrifying. Medical authorities had flawed understandings of the etiology of the disease, and often developed therapies that did little good and sometimes much harm in an unfortunate reversal of the Hippocratic Oath. Nevertheless, the intensity of cholera diminished, especially in the West, where industrialization eventually brought with it improved treatment of drinking water and the development of better sewage infrastructure. Well before researchers began to determine how the Vibrio cholerae pathogen functioned, an empirical understanding emerged of where cholera thrived and how it might be avoided. The gathering of humans, whether voluntary or not, into overcrowded sites where drinking water was suspect and sanitation poor proved deadly for millions. Trade emporia, whether seaports like Hamburg or caravan points like Berbera in Somalia, were dangerous. So too were pilgrimage sites such as Hardwar for Indian Hindus, Mecca for Sunni Muslims, and the Shiite Iraqi towns of Karbala and Najaf. Finally, the displacement of civilians and soldiers alike during military campaigns meant high risks for cholera and other infectious diseases. This held true for besieged towns in the Middle East or in the battlegrounds of the Russian and Austrian empires in the nineteenth century.