Early European cities were overcrowded and unsanitary, with disease spreading easily. The Industrial Revolution further overwhelmed cities with populations growing 40-70% per decade. Living conditions for the poor were incredibly unsanitary, with sewage and garbage flooding streets. Edwin Chadwick implemented reforms based on Jeremy Bentham's philosophy of helping the greatest number, including public water and sewer systems. Scientists like Pasteur, Koch, and Lister discovered germ theory, weakening the prior miasma theory of disease transmission and revolutionizing public health approaches. Haussman redeveloped Paris into wide boulevards and aqueducts, establishing a model for improving modern cities.