The Aztecs were an American Indian people and were the last ancient civilisation of Mexico during the 1400s and early 1500s. From their early beginnings as a small tribe, they rose to become one of the most important and advanced peoples of ancient America. Their economic and military strength enabled them to build a vast empire, conquering many other groups of people in Mexico. Tenochtitlan was the Aztecs' capital city, around 150,000 people lived there at one point. Religion was very important in the Aztec empire. The people worshipped hundreds of gods and fought wars not only to enlarge their empire, but also to get prisoners to sacrifice to the gods. The Aztecs built magnificent buildings (including pyramids) and had many artistic skills, carving sculptures out of stone such as the 'Calendar Stone'. The Aztec astronomers could tell very accurately from their calendar when eclipses of the sun or moon would occur. Other crafts which they were skilled at included pottery, woodcarving and weaving beautiful clothes, which were often decorated with gold and rare furs. The language that they spoke was Nahuatl, but they had no alphabet. Instead they used picture writing to keep records of events. The Aztec empire was finally destroyed by Spanish invaders in 1521.