Sigiriya is considered to be one of the most important urban planning sites of the first millennium, and the site plan is considered very elaborate and imaginative. The plan combined concepts of symmetry and asymmetry to intentionally interlock the man-made geometrical and natural forms of the surroundings. On the west side of the rock lies a park for the royals, laid out on a symmetrical plan; the park contains water-retaining structures, including sophisticated surface/subsurface hydraulic systems, some of which are working today. The south contains a man-made reservoir; these were extensively used from the previous capital of the dry zone of Sri Lanka. Five gates were placed at entrances. The more elaborate western gate is thought to have been reserved for the royals.