The Inca contributed in many ways. The main being they were engineers. This is a fact due to all the things they built, including civilizations. They built a system of roads and bridges across the roughest terrains of the Andes. Through their system of collective labor and the most advanced centralized economy, the Incas were able to secure unlimited manual labor.In less than a century, during the 1400s, they built one of the largest, most tightly controlled empires the world has ever known. Their skill in government was matched by their feats of engineering. Roads, walls, and irrigation works constructed by the Incas are still in use today.