A major obstacle to growth in early cities was the scarcity of water. The answer to this problem in many cases was an AQUEDUCT: a large, elevated stone "canal" that brought water from nearby hills directly into the city. This assured a convenient and dependable supply of fresh water to the city. AQUEDUCTS allowed cities to grow to unprecedented size, while at the same time they reduced the incidence of water-borne disease. Not only were larger cities now possible, but cities could be placed in otherwise inhospitable places, such as Los Angeles, which is located in a desert.