Prasat Prei Monti (Khmer: ប្រាសាទព្រៃមន្ទីរ) was erected on the eastern side of a vast domain (800 m by 500 m) surrounded by moats, which may have been the site of the capital city Hariharalaya (present-day Roluos) and of the royal palace of the time.
The decoration of the temple was left unfinished, only one lintel and a few colonettes were completed. The temple's main point of interest is a large rectangular-shaped cistern, or urn, 3 m (10') long and 2 m (7') wide, which was originally carved out of a monolith. It was found broken into several pieces and bricks were used during its restoration to replace the missing parts. The purpose of this unique structure is unknown, as the inscriptions carved on its edge are too eroded to be deciphered.