sentences:  Significant Maya sites of this Preclassic era of Mesoamerican chronology include Nakbé, El Mirador, Naachtun, San Bartolo and Cival in the Mirador Basin.Later, Petén became the heartland of the Maya Classic Period (c. 200 – 900 CE).At its height around 750 it is estimated that the Petén Basin was home to several million people, being one of the most densely populated regions of the world at the time.