The successors of Jayavarman II continually extended the territory of Kambuja. Indravarman I (reigned 877–889) managed to expand the kingdom without wars and initiated extensive building projects, which were enabled by the wealth gained through trade and agriculture. Foremost were the temple of Preah Ko and irrigation works. Indravarman I developed Hariharalaya further by constructing Bakong circa 881. Bakong in particular bears striking similarity to the Borobudur temple in Java, which strongly suggests that it served as the prototype for Bakong. There must have been exchanges of travelers, if not missions, between the Khmer kingdom and the Sailendras in Java, transmitting to Cambodia not only ideas, but also technical and architectural details.