Native America challenges everything we thought we knew about the Americas before and since contact with Europe. It showcases massive cities, unique systems of science, art, and writing, and 100 million people connected by social networks and spiritual beliefs spanning two continents and thousands of years. The series reveals some of the most advanced cultures in human history and the indigenous people who created it and whose legacy continues, unbroken, to this day.

Tonight's segment, Cities of the Sky, reveals the cosmological secrets behind America's oldest settlements. Scientists explore some of the world's largest pyramids and 3D-scan monumental mounds on the Mississippi River, while native elders describe ancient powers of the sky.

Watch it tonight at 9pm on WGBH World