Cambodia's gentle culture is influenced by Theravada Buddhism practiced by the bulk of its 13 million ethnic Khmer who live alongside substantial minorities of Chinese, Vietnamese, Cham Muslims and hill tribes. Angkor Wat, the ancient temple at the heart of a sprawling, monumental complex of stone block structures in Angkor, is a testimony to the power of the Khmer kingdom, which peaked during the 11th century. The four years of nightmarish Khmer Rouge rule led to the state-sponsored extermination of citizens by its own government. Between 1 million and 2 million people were massacred on the “killing fields” of Cambodia or worked to death through forced labour. Pol Pot's radical vision of transforming the country into a Marxist agrarian society led to the virtual extermination of the country's professional and technical classes.