Continuing on his way to the center of the temple, the visitor passes through a series of massive enclosure walls; these walls recreate sacred mountain ranges, symbolic of obstacles that must be overcome on the path to enlightenment (green highlights in Fig. 1). Monumental tower gateways, called gopurams, grant the visitor passage through the walls, each successive one revealing a more sacred area, farther removed from the outside world.
The combination of concentric enclosure walls with large gateways was derived directly from South Indian Hindu architectural precedent. Enclosure walls make their first appearance very early in the Khmer building tradition — at the late 9th century pre-Angkor site of Roluos in the temples of Preah Ko, Bakong and Lolei — and are a constant feature in all subsequent temples.