The Archaic period was a time of significant architectural creativity. The temples, its most important structures, grow more elaborate and subjected to strict symmetry. The wooden elements of the top building were gradually replaced by stone, and new construction techniques were created. The end of the Archaic period is usually dated from about 600 to 500 BC. During the Archaic period, new types of buildings appeared in the American continent. They are called "Archaic" because they are built without using bricks or concrete. These buildings are made of wood and have flat roofs with no walls except for some special cases. The doors and windows are made of wood too. In warmer climates, such as in North America, these buildings had only one floor. But in colder regions, such as in Europe, they often had several floors. People used trees as a source of fuel and for building materials. They built their houses out of either log cabins or plank buildings. There was no iron tooling at this time. People made do with what nature provided them. As you can see, the American continent was not inhabited yet by humans. It was still being discovered by different cultures who moved there looking for land and resources. The first people came to America around 20,000 years ago. Scientists think that they may have come from Asia through either a southern or northern route.