Chan Chan was the capital of the Chimu kingdom, the chief state in Peru before the establishment of the Inca Empire. The Chimu kingdom reached the height of its power in the fifteenth century, not long before falling under the Incas. The planning of this huge city, the biggest in pre-Colombian America, reflects an elaborate system of social-class stratification.
The center of the city is divided into nine walled "citadels," each constructed out of adobe brick finished with mud, and each containing temples, cemeteries, gardens, reservoirs and symmetrically arranged rooms. These citadels, it is believed, were the living quarters, burial places and warehouses of the aristocracy. The bulk of the city's population, however, lived outside of the citadels in much more modest quarters
Because these remnants of a complex culture and society require continuous protection from natural erosion, the abandoned and fragile site of Chan Chan was inscribed on the World Heritage List in 1986.
I can't recall exactly what this is, but I think it might have once been a natural water source/reservoir - but I might be wrong :P