People first arrived in North America from Asia via the Bering Land Bridge, migrating south over time. Pre-Columbian America had many diverse native cultures that developed different ways of life based on their environments and resources, as seen in the housing, clothing, and farming styles of groups like the Plains Indians, Northwest Coast Indians, and Eastern Woodlands tribes. Archaeologists study the ruins of ancient civilizations as primary sources to understand pre-contact cultures, relying on artifacts, structures, and documents from the time period.