EUROPEANS CONQUERED MOST OF TROPICAL AFRICA between 1880 and the First World War. This was also a period of rapid advance in tropical medicine. Malaria was by far the most serious threat to Europeans living in the African tropics, and the mosquito theory made its appearance just when colonial administrations were struggling to keep soldiers and administrators alive in a difficult environment. New currents in European thought about urban planning flourished in these same years-the key period for city planning in Africa, when colonial capitals were either founded or redesigned. The play of these crosscurrents of thought during a period of crucial decision making offers an interesting example of ideas in action, one with implications for our understanding of human behavior both in Africa and beyond. Europeans had been applying their medical ideas to the African scene since at least the early nineteenth century. Through mid-century they were especially concerned with medical topography-studies of particular locations, soils, temperature, and rainfall to determine what makes a place healthy or unhealthy. Some of the things they concluded were true; others were not. They had known for centuries that high altitudes meant cooler weather, and they associated heat with putrefaction and hence with disease. In India, officials had retreated to the "hill stations" in the warm season since the beginning of the century. But they also sought protection at much lower elevations, in the belief that malaria in particular was caused by emanations from the soil, which crept "assassin-like close to the earth."' One solution was simply to put houses on stilts, elevating them ten to fifteen feet above the ground. That was a common prescription for tropical housing in India and the West Indies as well as in Africa. So was the idea of putting military camps in high places whenever possible. In 1863, following the Sepoy Mutiny of 1857 and the sanitation scandals of the Crimean War, a royal commission gathered evidence and issued detailed recommendations for sanitation reforms in India. These and other reforms reduced the death rate from disease of British soldiers serving in India from about 50 per 1000