The Maya is a Mesoamerican civilization, noted for the only known fully developed written language of the pre-Columbian Americas, as well as its art, architecture, and mathematical and astronomical systems. Initially established during the Preclassic period (c. 2000 BC to 250 AD), many Mayan cities reached their highest state development during the Classic period (c. 250 AD to 900 AD), and continued throughout the Postclassic period until the arrival of the Spanish. At its peak, it was one of the most densely populated and culturally dynamic societies in the world.