Complex sentence: In the Late Classic period Cotzumalhuapa was an important power in Mesoamerica and formed one gigantic city with over ten square kilomters of extension and it included the smaller archeological sites "El Baúl" and "Bilbao" and "El Castillo".
Split into simpler sentences: In the Late Classic period, Cotzumalhuapa was an important power in Mesoamerica. Cotzumalhuapa covers over ten square kilometers and includes the smaller archeological sites "El Baúl" and "Bilbao" and "El Castillo".