At some point around 800 the city was invaded by Toltec people from the north, who exerted a strong influence of the subsequent building styles. The Toltecs are the people who built Teotihuacan near Mexico City. Besides using round buildings and pillars, the Toltecs were more warlike than the Mayan and seemed to have a stronger propensity to employ human sacrifice. This fierceness and ritual difference speaks through the art and architecture of Chichen.

El Castillo is a time temple that sheds light on the Mayan astronomical system It was built in 800 just before the Toltec invasion. An impressive 78 feet tall, the temple's name means castle in Spanish. El Castillo was actually a huge solar calendar. If you did the math, you would find that the 91 steps on each side, times 4 for each side and each season, plus 1 for the crowning platform adds up to 365 -- one step for each day of the solar year. During the equinoxes, the shadow pattern of the pyramid's steps seems to show a serpent climbing up the steps in March, and down the steps in September.

The Ball Court is the largest and finest in Mexico. At 272 feet by 199 feet, it's about as long as a football field and little bit wider. On the south side is the tribune, a raised platform that may have been used for dance performances. Maybe even half-time entertainment. A Maya prophesy states that on December 12, 2012, the great warrior serpent Kukulkan will rise out of the playing field and end the world.

El Caracol means giant conch shell because of its circular, spiraling design. The windows in observatory dome are aligned with certain stars on specific dates. This is where the priests decreed the dates for rituals, celebrations, corn planting, harvests. This building especially displays the brilliance and precision of Mayan astronomy.