Roluos Group was the capital of Indravarman I (877 to 889). The monuments of Roluos are located 13 km from Siem Reap. This group consists of Preah Ko, Bakong and Lolei. Built during the reign of Indravarman I, the late ninth century, Roluos Group are the first temples "hard" built by the Khmers and represent the beginnings of classical architecture and art in Cambodia.
The Preah Ko (Sacred Bull) derives its name from the three statues of sandstone located in the front of and facing the temple's central towers. These statues represent Nandi, the white bull who serves as the mount of Shiva. Preah Ko consists of six brick towers arranged in two rows of three towers each perched on a sandstone platform. This temple was built in honor of the king's ancestors.
The Bakong in Roluos group is one of the first mountain temples of Khmer architecture. This temple-mountain represents Mount Meru, a sacred mountain in Hindu and Buddhist cosmology and center of all the physical, metaphysical and spiritual universes. Bakong has a pyramid shape and is built entirely of sandstone. Bakong also houses a beautiful Buddhist monastery that is still active.
The Lolei is a Hindu temple built by Yasovarman first. Lolei consists of four brick temple towers grouped together on a terrace. The king built Lolei for his ancestors: one for his grandfather, one for his grandmother, one for his father, and one for his mother.
Once an island temple, Lolei was located on an island slightly north of centre in the now dry Indratataka baray, construction of which had nearly been completed under Yasovarman's father and predecessor Indravarman I. Scholars believe that placing the temple on an island in the middle of a body of water served to identify it symbolically with Mount Meru, home of the gods, which in Hindu mythology is surrounded by the world oceans.