Here is a tragedy of the megacity. In Cairo in 1998, less than 50 percent of its sewage was treated; flowing directly into the groundwater table, producing over decades an acidity that ate the stone foundations of its beautifully sculpted, ancient Islamic monuments. Automotive and industrial air pollution rendered the rain so caustic that accumulated chemicals attacked the upper parts of structures too. Extended poverty drained building maintenance. Rampant population growth magnified the density and wear within each edifice. Eventually, the stonework of numerous great landmarks crumbled to the touch—from a city where the diversity of enlightened social institutions, universities, libraries, hospitals, were unmatched by medieval European counterparts.