UNESCO has Phimai designated as a World Heritage Site for future listing and the following is its description and reason for the designation.'' Phimai or Vimai was the name of a large rectangular ancient Khmer city surrounded on all sides by boundary walls and moats, lying 260 kilometers northwest of Angkor. Prasat Phimai was the Mahayana Buddhist sanctuary situated at the center of the city. Prasat Phimai itself together with the Cultural Route and the associated temples of Phanomrung and Muangtam are among the finest Khmer monuments and constitute a testimony to the civilization, prosperity and wealth, and the power of the Khmer Empire at its peak. From Phimai the historical route stretched out Southeast into the southern sub-region of the Khorat Plateau leading to the pass across the Phnom Dongrak mountain range on the Thai-Cambodian border. In the ancient time of the Khmer Empire, travelers and pious pilgrims taking this route, which connected Angkor to Phimai, had at their disposal rest houses spanning over the route as well as some hospitals along the route. The remains of these rest houses and hospitals mark out Phimai 's unique cultural route, covering approximately a distance of 150 kilometers.
Prasat Phimai was originally built in the l l t century after a large part of the Buddhist Kingdom of Dhvaravadi was conquered and became the domain of the Khmer Empire. It is evident from the statuary of Phimai that it was built as a Mahayana Buddhist sanctuary. The inscriptions inside the principal tower also signify the Buddhist origin of Phimai, praising Lord Buddha and mentioning the name of King Suriyavaraman I as a Mahayana Buddhist, as well as specifying the years corresponding to the Buddhist Era of 1579 and 1589 ( 1036 and 1046 AD ). It is significant to note that other Khmer temples belonging to the same era, such as Angkor Wat or Prasat Phanom Rung, all were built as Hindu temples, the unique Buddhist sanctuary of Phimai being the single exception. Besides the Buddhist temple of Bayon in Cambodia, Phimai was duly recognized as the most important full-fledged Khmer Buddhist sanctuary by Jayavaraman VII the Great, who was a renowned fervent Buddhist.
The plan of the township was in the shape of a rectangle enclosed on all sides by moats and surrounding walls, of which traces still remain. Of the four walls, the front side of the ancient town stood, as the Temple itself, facing Southeast in the direction of Angkor. The fact that the temple of Phimai faces Southeast in the direction of Angkor instead of facing east, which is the common feature of other Khmer temples, is significant, the reason however, is unknown. It might have been by design to give effect to the special position and importance of Phimai in its relationship to Angkor, as made evident later by the command of King Jayavaraman VII to build rest houses and hospitals on the cultural route to Phimai.
The restoration of Prasat Phimai from 1964 to 1969 with the technical assistance from the French Government was supervised by Prince Yachai Chitrabongse and M. Bernard Phillip Groslier, who was the director of the restoration work at Angkor. The lintels on the inside of the buildings, depicting scenes of the life of Buddha as well as episodes from the Ramayana, are among the foremost of Khmer art. A very fine sandstone statue of King Jayavarman VII in meditation was also found inside of one of the buildings.