These early groups are known as Hohokam, Adenans, Hopewellians, and Anasazi. They built villages and grew crops. Their lives were connected to the land. Family and community were important to them. History shows they told stories and shared information mostly by talking, not writing. Some used a form of picture writing called hieroglyphics. Nature was important to their spiritual beliefs. Some groups built big piles of earth in the shapes of snakes, birds, or pyramids. The different groups traded with each other, but they also fought. No one knows why, but these groups disappeared. Other groups, Hopi and Zuni, later came to this land and prospered. By the time the first Europeans arrived, about two million native people lived in what now is the United States.