MEXICO CITY—In 1519, Hernán Cortés and his conquistadors arrived in Cholula, one of the largest cities in central Mexico. Roughly 50 miles southeast from modern day Mexico City, its tens of thousands of residents sat in the shadows of the 17,000 foot Popocatépetl volcano. It had a temple featuring more stairs, claimed one Spaniard, than the main pyramid in Tenochtitlan. …