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In Cambodia, Buddhist temples were built between the 9th and the 13th centuries by a succession of 12 Khmer kings. Angkor spreads over 120 square miles in South-East Asia and includes many major architectural sites. In 802, when construction began on Angkor Wat, financed by wealth from rice and trade, Jayavarman II took the throne, initiating an unparalleled period of artistic and architectural achievement, exemplified in the ruins of Angkor, center of the ancient empire. Here Angkor Wat, the world's largest temple, an extraordinarily complex structure filled with iconographic detail and religious symbolism, is sited. It was ultimately abandoned in the 15th century because of internecine rivalries and left to the ravages of time. It does, however, retain its orientation to the stellar axes and markers of the solstices; it's a means of orienting a holy form that serves the continual acknowledgement of deities and the stories of history, most markedly the Mahabharata and the Ramayana. The culture of South India has made its mark here; it's remarkable how the parts of the day are honored with the gods watching over all, prayers wafting to the sky.
Built in the later part of the 12th century by Jayavarman VII (the last king), Ta Prohm has been overtaken by jungle and is only now being slowly restored to its initial form. It has a smaller presence than the other temples, and is not as elaborate. The roots of the invading trees have crawled into the structure to the point that their removal would result in the collapse of the structure, so not all of this temple will be resurrected. It will remain firmly embedded in the Cambodian jungle as a reminder of an old civilization that failed to conquer the natural world for long and then passed into history. As have all the old civilizations. As will ours.
Update 3/24/16: The origins of Angkor Wat