Listeros,

An international team of researchers at the University of Nevada have
used stalagmites to study the climate in Mexico over 2,400 years. The
rise and fall of Mesoamerican civilizations are linked to rainfall in
this study. The report will appear in the journal "Geology." The team
analyzed a stalagmite in Juxtlahuaca Cave in Guerrero. Stalagmites are
ancient rain gauges. They grow more rapidly than tree rings and leave
a longer record. Stalagmites can be used to determine climate
variations on an annual timescale. There was above average rainfall in
Mexico, according to the stalagmite record, between the 1st and 3rd
centuries when Teotihuacan rose to power. Then came a 500 year drying
period with a drought of 150 years coinciding with population decline
at Teotihuacan at 550 CE, when springs dried up there.

The Sacramento Bee has the story here;
http://www.***.com/

Mike Ruggeri's Teotihuacan; City of the Gods
http://www.***.com/