Complex sentence: It has an occupation dating predominantly from the Middle Preclassic (900--600 BC) period of Mesoamerican chronology, and at its peak was one of the largest known Mesoamerican sites of that era.
Split into simpler sentences: It has an occupation dating predominantly from the Middle Preclassic (900--600 BC) period of Mesoamerican chronology. At its peak, this was one of the largest known Mesoamerican sites of that era.