The Spanish conquistadors Pedro de Alvarado and reached Chalco in the fall of 1519. The Chalca allied with the Spaniards and participated in the defeat of the Aztecs. Hernán Cortés claimed Chalco for himself as an encomienda, but failed to maintain his possession of it. Chalco was designated a corregimiento by 1533. Several places outside the traditional region of Chalco were added to it in colonial times.