The order imposed by Teotihuacan during the Classic period gave way to the fragmentation of power among such city states as Cholula, Xochicalco and El Tajin . The Post-Classic period began about 900 A.D., in which, with the exception of metallurgy, was inferior to the Classic period in intellectual, artistic and scientific advancements .Even metallurgy was mainly used for making jewelry, with no metal farming implements or weapons being made .   In the Post Classic period saw the rise of warrior dominated militaristic societies demanding tribute from vassal states . In religion there was growing importance of gods who demanded ' divine liquid'  ( human blood ) to keep the natural balance and the Sun to continue to shine .   Rise of the Toltecs   the famous Toltec warrior statues, known as the Atlantes   When Teotihuacan was powerful, it acted as a buffer between the cultures of the Valley of Mexico and the nomadic peoples to the north .With its downfall, nomadic warriors entered the area from the north .There were many groups in this northern area, known collectively as Chichimecs ' People of the Dog Lineage .' The most powerful of these were the Toltecs, who probably originated in southern Zacateacas .At the beginning of the 10th century, a great Toltec leader known as Mixcoatl ( Cloud Serpent ) who conquered many cities in the valley and set up his capital at Culhuacan . Mixcoatl was murdered by his brother, who assumed control . Mixcoatl's pregnant wife fled into exile and gave birth to a son names Ce Acatl Topiltzin who would become an important hero in ancient Mexico .The boy became a priest of Quetzacoatl and attaining manhood gathered about them those still loyal to his father and killed his father in single combat and made himself ruler of the Toltecs .Around 968 A.D.. he moved his capital to the frontier and founded the city of Tula .   pyramid of the warriors, Tula   This was to become the most important city in Mexico between the fall of Teotihuacan and the rise of the Aztec Tenochtitlan .Their hegemony would only last 200 years, but had profound influence on the Aztecs, who ascribed to Ce Acatl Topiltzin all the benefits to mankind such as agriculture, writing and the calendar.   Ce Acatl Topiltzin, faced trouble at home. His city was made up of people from other Chichimec tribes and the priests of the tradition militant supreme god of the Toltecs Tezcatlipoca ( Shining smoke ) resented the ascension the foreign god Quetzacoatl .   According to legend, Tezcatlipoca in disguise, entered the palace of Ce Acatl Topiltzin, who was ill. Tezcatlipoca , offered Ce Acatl Topiltzin medicine, which was in fact pulque , a strong alcoholic drink made from cactus juice. Ce Acatl Topiltzin became drunk, and the next morning found he had slept with his sister, both of which were against the vows of a priest of Quetzacoatl. He went into exile , according to legend, as he left for exile he and his followers marked their way by shooting arrows in saplings, creating crosslike signs . He vowed he would return from where the sun rose and retain his throne in the year Ce Acatl, which recurred cyclically. He was said to be fair skinned and had a beard, a rarity in Mexico . This important legend was to have disastrous consequences for the Aztecs 500 years later in 1519, the year of Ce Acatl, when the Spanish arrived .   With the return to power of the militant Tezcatlipoca faction, the importance of the warriors and their god can be seen in the architecture of Tula . The famous towering statues of the Toltecs were made of warrior figures 18 feet tall,some of which are devouring human hearts .  Quetzacoatl only demanded sacrifices of butterflies and small animals, Tezcatlipoca demanded human sacrifice .Under these aggressive warriors the Toltecs created an empire as large as that of Teotihuacan .In the late 11th century drought and famine struck and eventually the people abandoned Tula. Once again the Valley of Mexico was undefended against the nomads of the north .