In size and sophistication, the most impressive empire in the Americas was the Incas. Established in Peru in the twelfth century, the Incan empire united millions of people and dozens of distinct cultures under a single governing system. The Incas lacked what many assume are essential to empire-building: writing, the wheel, a favorable climate. Still, the Incas overcame these challenges with incredible science, technology, engineering, and math or STEM innovations. These included terrace agriculture, elaborate road systems, earthquake-proof buildings, a planned economy without money, and an elaborate mathematics communicated with textiles. Incan accomplishments show that technological developments take many unexpected forms and will inspire your readers to think outside of the box.