The northern section, nearest the sacred cenote, was built later during the time of Mexican (Toltec) influence from 900 A.D. - 1200 A.D.  The style of the northern section shows a mix of Mayan and Mexican elements.   It is believed that Chichen-Itza might have been the capital for the uneasy alliance of Mayan - Mexican invaders that dominated the area and contributed to the social unrest that played a large role in the downfall of the Mayan civilization.