Historians have long attributed the sharp decline in nineteenth-century urban mortality to advances in medicine. A competing account, now widely favored, credits instead the unglamorous work of sanitary engineering: sewers, filtered water, and refuse collection. Its proponents note that death rates in several cities fell steeply decades before the germ theory of disease was accepted, let alone before effective drugs existed—a sequence the medical explanation struggles to accommodate. Skeptics counter that sanitation itself was often justified by emerging medical ideas, so the two causes are entangled rather than rival. Yet even they concede that clean water did its work whether or not the officials who supplied it understood why, a concession that tilts the balance toward the engineers.