Indians have a long and rich history of civilization, among which three important civilizations are Maya civilization, Aztec civilization and Inca civilization. Maya civilization is located in today's Central America and Mexico, and its cultural and technological development has reached a brilliant peak. They built magnificent cities and temples, made accurate astronomical observations and created a unique calendar system. The Mayans also made important contributions to agriculture, mathematics, art and writing. The Aztec civilization originated in present-day central Mexico. They built huge cities and developed a highly organized social structure and religious system. The Aztecs make a living from agriculture, handicrafts and trade, and their art and architectural style are also unique. Inca civilization flourished in the Andes of South America. They are famous for building complex stone buildings and powerful land management systems. The agricultural technology of the Incas is very advanced. They use terraced fields and irrigation systems to increase the yield of crops. In addition, they have developed a complex transportation and communication network.