The Maya is a Mesoamerican civilization, noted for Maya script, the only known fully developed writing system of the pre-Columbian Americas, as well as for its art, architecture, and mathematical and astronomical systems. Initially established during the Pre-Classic period (c. 2000 BC to AD 250), according to the Mesoamerican chronology, many Maya cities reached their highest state of development during the Classic period (c. AD 250 to 900), and continued throughout the Post-Classic period until the arrival of the Spanish. The Maya civilization shares many features with other Mesoamerican civilizations due to the high degree of interaction and cultural diffusion that characterized the region. Advances such as writing, epigraphy, and the calendar did not originate with the Maya; however, their civilization fully developed them. Maya influence can be detected in Honduras, Belize, Guatemala, and western El Salvador to as far away as central Mexico, more than from the central Maya area. The many outside influences found in Maya art and architecture are thought to have resulted from trade and cultural exchange rather than direct external conquest. The Maya peoples survived the Classic period collapse and the arrival of the Spanish conquistadores and 16th-century Spanish colonization of the Americas. Today, the Maya and their descendants form sizable populations throughout the Maya area; they maintain a distinctive set of traditions and beliefs resulting from the merger of pre-Columbian and post-Conquest ideas and cultures. Millions of people speak Mayan languages today. In 2005 the Rabinal Achí, a play written in the Achi language, was declared a Masterpiece of the Oral and Intangible Heritage of Humanity by UNESCO.