 As of 2006, Chalco included part of the world's largest mega-slum, along with Ciudad Nezahualcoyotl and Ixtapaluca.Archeologists date human settlement around Lake Chalco from about 2400 B.C, but major settlement occurred at approximately 1240 B.C., when the first tribe to call itself "Chalca" migrated to the region.This tribe was followed by others, ethnically and linguistically diverse, who added the name Chalca to their own.