The Mayan civilization by this point is in its post-classical period. Its classical period is in bold right over here, but there are still many independent Mayan city-states in the Yucatan Peninsula, but the two notable empires here are the Aztecs and the Incas, which form in the 15th century. What makes them an empire is that you have one group, in the case of the Incas, the Kingdom of Cusco, conquering other peoples and taking tribute from them. Now what was interesting about the Incas is that they were able to form this large empire, the largest empire in the Americas at the time of the European conquest. This empire had 10 million people in it, and what's amazing is that you have this large, powerful empire with significant building projects. This is a picture of Machu Picchu. Historians believe that it was built as an estate for Pachacuti, so they were able to do the sophisticated construction despite not having a written system as we know it.