At the time of European contact, the indigenous peoples of the Americas had created some of the most sophisticated civilizations in world history. Aztec engineers reconstructed the giant lake in the central basin of Mexico. They understood the principles of water salinization and built engineering features to protect a good portion of their water supply. Inca engineers built bridges that spanned vast canyons and a road system that may have reached as long as 40,000 kilometers, according to John Hyslop. Maya scholars excelled in mathematics and astronomy, making precise calculations of the planetary bodies. Massive irrigation canals over 50 kilometers in length were built through harsh deserts and mountainous terrain by the Moche, Chimu, and Inca peoples of Peru from the middle of the first millennium CE to the middle of the second. The ancient peoples of the Americas also excelled in architecture, metallurgy, boating technologies, and many other achievements that required precise scientific knowledge.