No. 50: Mar-Apr 1987
One of Tiahuanaco's (or Tiwanaku's) many puzzles has been how food for such a large city was grown at an altitude of circa 3,850 meters (12,600 feet) in the frosty, windswept Bolivian Andes. This problem along with the fabulous stonework and extensive ruins have precipitated theories involving extraterrestrial visitors and an age for the site in the hundreds of thousands of years.
At least the food-supply puzzle now seems to be in hand. Stereoscopic aerial photographs show in startling detail:
"...immense, curvilinear platforms of earth...these fields form elevated planting surfaces ranging from five to 15 meters wide and up to 200 meters long...Extensive and nearly continuous tracts of these fields -- all of which have been abandoned for centuries -- run from the edge of Lake Titicaca to about 15 kilometers inland, and form virtually the only topographic relief in the broad, gradually sloping plain."
Some of the raised fields are remarkably sophisticated in design. At the base is a layer of cobblestones for stability. These are covered by a 10-centimeter layer of clay. On top of the clay are three distinct layers of sorted gravel; all capped by rich organic topsoil. These fields were simultaneously an aquifer for the fresh water percolating down from the surrounding hills and a barrier to the brackish water from Lake Titicaca. Even at Tiahuanaco's altitude, these fields could have grown potatoes, oca, or ulluco and the chenopod grains, as well as quinowa and caniwa. Tiahuanaco and its satellite cities could have been fed with enough left over for export. Not bad for farmers 2,000 years ago!
(Kolata, Alan L.; "Tiwanaku and Its Hinterland," Archaeology, 40:36, January/February 1987.)