Chankillo Archaeoastronomical Complex

Thirteen towers on a ridge told time for an entire society. At Chankillo in Peru's Casma Valley, built around 250–200 BC, observers stationed at points either side of the tower line could track sunrise and sunset along the horizon, fixing any date of the year to within a day or two — solstices and equinoxes included. With its triple-walled Fortified Temple, the complex is the oldest known solar observatory in the Americas. UNESCO inscribed it in 2021.