The first great temple mountain was the Bakong, a five-level pyramid dedicated in 881 by King Indravarman I. The structure of Bakong took shape of stepped pyramid, popularly identified as temple mountain of early Khmer temple architecture. The striking similarity of the Bakong and Borobudur in Java, going into architectural details such as the gateways and stairs to the upper terraces, strongly suggests that Borobudur might served as the prototype of Bakong. There must have been exchanges of travelers, if not mission, between Khmer kingdom and the Sailendras in Java. Transmitting to Cambodia not only ideas, but also technical and architectural details of Borobudur, including arched gateways in corbelling method.