Mayan civilization in the Lacandon area is marked by rising exploitation of rain forest resources, rigid social stratification, fervent local identity, waging war against neighboring peoples. At its height, it had large cities, a writing system, and development of scientific knowledge, such as mathematics and astronomy. Cities were centered on large political and ceremonial structures elaborately decorated with murals and inscriptions. Among these cities are Palenque, Bonampak, Yaxchilan, Chinkultic, Toniná and Tenón. The Mayan civilization had extensive trade networks and large markets trading in goods such as animal skins, indigo, amber, vanilla and quetzal feathers. It is not known what ended the civilization but theories range from over population size, natural disasters, disease, and loss of natural resources through over exploitation or climate change.