Tiahuanaco

" Thin air drops the ambient temperature to below freezing at night causing a frost that kills most plants. Recently, however, an aerial survey of the site revealed the solution. Multiple grid and maze like structures throughout Tiahuanaco, visible only because of the discoloration of the underlying soil, were discovered to be an ancient network of gardens and canals, capable of growing potatoes and other crops.

The plan was ingenious. Canals were placed in grids that surrounded the narrow gardens. The depth of these canals was kept to from 24 to 30 inches so that the strong daytime sunlight could easily warm the water. In the evening, when the frigid air caused frost, the canals vented their stored heat in the form of a fog. This kept the temperature around the plants elevated above freezing and also helped irrigate them."
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