The Maya are an ancient civilization, which dominated the vast area currently entitled Central America and Mexico. They rose circa 600 B.C. and fell circa 900 A.D., due largely in part to political upheaval and the demise of many city-states. The people of its time created advanced architecture and art and produced styles of math and astronomy, which contrasted those of the Hindu and Arab nations. The ancient Maya of the Yucatan considered cenotes (pools and cave rivers), a sacred entrance to the underworld. It was believed that once an individual entered such a place, one would not die, but rather be taken to the underworld in harmony. Often, when drought, war or other dangers threatened, the Maya would engage in body piercing and collect ones blood on parchment and burn it as an offering. More radical sacrifices occurred when a high priest would open a mans chest, and retrieve a beating heart. Evidence of this can be seen when viewing the rib fractures of a man due to the fact that, " ripping out the heart cause[s] breaks from the inside out."(Vesilind, 91). Further evidence of human sacrifice made to the cenotes was found when diver Arturo Gonzalez had discovered a young man's skull. Gonzalez, and two other individuals, Alejandro Terazas, a physical anthropologist, and Carmen Rojas, a young archaeologist are part of the Underwater Archaeology Area of Mexico's National Institute of Anthropology and History (INAH), and are co-directors of the research project. Terazas also discovered further evidence of human sacrifice when he observed the skull of a 25-year-old man obtained from the Yucatan waters. He observed the individual had, " died violently. [T]he process of removing the muscles from the top of the victim's head down the face", was clearly evident. (Vesilind, 88) Many of the cenotes were formed as a result of a meteor, which hit the earth 65 million years prior. It is thought to be the same meteor, which lead to the extinction of the dinosaurs.