As early as 30,000 years ago, small groups of Paleolithic hunters and gathers reached north America from Asia. This migration took place during the last ice age. Many historians believe they followed herds of bison and mammoths across the land bridge. Global Warming occurred 10,000 years ago when the climate grew warmer. As the Ice sheet melted water levels rose covering the land bridge. Earliest American civilization emerged in the tropical rain forest along the Mexican Gulf Coast. Olmec civilization lasted from about 1400 B.C. to 500 B.C. -Archeologist know very little about the Olmecs. However, rich tombs and temples suggest a powerful class of priests and aristocrats stood at the top of Olmec society. -The most dramatic remains of the Olmec civilization are the giant carved stone heads found in the religious center at La Venta. No one knows how the Olmecs moved the 40-ton stones from distant quarries. Between 300 and 900 A.D. the Mayans flourished. Mayan city-states flourished from southern Mexico through much of Central America. Farming method of the Mayans allowed them to flourish in a tropical environment Towering pyramid temples dominated the largest Mayan city of Tikal (present day Guatemala) Priests performed sacrifices on these pyramids as ordinary people watched. Mayan pyramids remained the tallest structures in the Americas until 1903. Much of the wealth of Tikal and other cities came from trade. Each city had it own ruling chief. He was surrounded by nobles who served as military leaders and officials who managed public works. Mayan rulers were usually men but Mayan records show women occasionally were rulers. Most Mayans were farmers, they grew corn, beans and squash. As well as fruit trees, cotton, and tropical flowers. Men cultivated the crops while women turned them into food. To support the cities farmers paid taxes in food. They developed an advanced hieroglyphics. Many scribes kept records in books made from bark. In order to measure time precisely, as result they developed a 365 day calendar. Mayan priests invented a numbering system and understood the concept of zero. About 900 A.D. Mayans abandoned their cities, leaving great stone palaces and temples swallowed up by the jungle. No one knows for sure why Mayan civilization declined. Possibly frequent warfare forced the Mayans to abandoned their traditional farming methods, or over population and over cultivation. Today millions of people in Central America speak the Mayan language. Long before the Mayan cities rose to the south the city of Teotihuacán emerged in the valley of Mexico. From 100-750 A.D. Teotihuacan dominated this large area. The city eventually fell to invaders but its culture influenced later peoples especially the Aztecs Until the late 1200’s the Aztec people were nomads. The would switch from hunters to farmers. They built the city of Tenochtitlan which is present day Mexico City. As their population grew they found new ingenious ways to create more farmland. They built Chinampas, or artificial islands made of earth piled on red mats that were anchored to the shallow lake bed. They raised a lot of corn, squash, and beans In the late 1400’s Aztecs greatly expanded their territory. Through conquests and alliances they spread their rule across most of Mexico. By 1500 the Aztecs had an estimated 30 million people in their empire. War brought immense wealth and power. Tribute or payment from conquering people help the Aztecs turn their capital into magnificent city. When the Spanish reached Tenochtitlan in 1519 they were amazed at its magnificence. The leader of the Spanish expedition was Hernan Cortes. Aztecs had a single ruler over all its empire and below him were nobles served as judges, and governors of conquered provinces. The Majority of people were commoners who were farmers. At the bottom of society were slaves who were criminals or prisoners of war. Slaves did have rights, for example they could own land and buy their freedom. Priests were a class apart. They performed rituals that they believed pleased Aztec Gods and prevented droughts or other disasters. Huitzilopochtli, the Aztecs believed would battled forces of darkness each night and was reborn each morning. As legend of the sun shows, there was no guarantee that the sun would always win. To give sun the strength to rise each day, Aztecs would offer human sacrifices. Aztecs offered tens of thousands of sacrifices by offering the hearts of their victims.