Dey Rolous Thom ដីរលួសធំ
Roluos is a village with a group of monuments anterior to those in Angkor. The Roluos group is what has remained from the ancient Hariharalaya, which was the first significant capital during the Khmer Empire of the Angkorian era. The Sanskrit name Harihara-alaya means "Harihara-abode". Harihara is a Hindu deity being half Shiva, half Vishnu.
Hariharalaya was established as a capital already by the empire founder Jayavarman II, but soon afterwards left by this king, who changed his residential town quite often. His successor Jayavarman III, of whom little is known, seems to have resided in Roluos in the area of Prei Monti, a rarely visited very early temple with three towers, now in ruins.
The even more isolated single temple tower (Prasat) called Trapeang Phong is the first Khmer monument decorated with female half-deities called Devatas, later on often ifentified with Apsaras. (Apsaras are a kind of Devatas usually depicted dancing or flying, the term "Devata" is more accurate for a sculptural reliefs of an upright standing semi-goddess.) Trapeang Pong may even be from the earlier period of Jayavarman II in the first half of the 9th century.
Actually, it is Indravarman I in the late 9th century who became the founder of what can be seen in Roluos today. Preah Ko, giving its name to the art style of Indravarman's reign, is this king's ancestor temple belonging to his palace compound. Even more innovative and examplary for future temple mountains in Angkor is the step pyramid called Bakong, which was Indravarman's state temple. Temple ensembles in Roluos, consisting of Prasats and other sacred buildings, were surrounded by concentric enclosure walls, for the first time in Khmer architecture, setting the pattern for the entire Angkorian era. The entrance pavilions called Gopurams, crossing the enclosure walls at cardinal points, were invented at Indravarman's Roluos temples, too. Gopurams sheltered the guardian deities or the sanctuary. For the first time, library buildings were built of non-perishable materials instead of wood. The function of those library edifices so typical for Angkor is still under debate, but inscriptional evidence and comparison with later Thai temples confirms that the term "library" may be completely adaequate, since holy scriptures of monasteries were kept in separate buildings. Nevertheless, libraries may have been sacristies for other devotional objects as well.