The houses ringing the stupa comprise a huge bahal (average diameter 120 m (394 ft)). The stupa itself is a symbol of enlightenment and at Bodnath the symbolism is particularly clear. Each different shape represents one of the five elements, earth, water, fire, air and sphere, which are also the attributes of the five Buddhas. Brought together in the form of the stupa, their unity reflects in abstract fashion the structure of the universe itself.The stupa's nine levels represent Meru, the World Mountain, seat of the gods and center of the cosmos. At Boudha an irregular sixteen-sided walled enclosure surrounds the base of the stupa, which consists of three platforms, decreasing in size, their rectilinear pattern symbolizing Earth. Next come two circular plinths supporting the hemisphere of the stupa, symbolizing water, and above that a tower, the four faces of its cuboidal shaft bearing the eyes of the omnipresent god. Between each pair of eyes is the "third eye", symbol of wisdom. The 13 steps of the pyramid surmounting the shaft represent the ladder to enlightenment, the triangular shape being the abstract form for fire. At the top of the tower is a gilded canopy, the embodiment of air, with above it a gilded spire, symbolic of the sphere.In northern Buddhism, as practiced in Tibet and neighboring countries, the stupa is also a representation in three dimensions of the mandala of the five Dhyani Buddhas, four of whom mark the cardinal points around the base of the stupa. The fifth, Vairocana, sits inside the hemisphere itself. Like most Buddhist images the five Buddhas personify phenomena, in this case the five cosmic elements.At Boudha the main access to the upper platform is on the north side where Amoghasiddhi, progenitor of the future Bodhisattva, presides. Below Amoghasiddhi is the not yet immortal Buddha Maitreya, the future Buddha or Buddha-to-be.In addition to its general significance the stupa at Boudha is closely associated with the cult of Bodhisattva Avalokiteshvara (Padmapani). The 108 forms of the Bodhisattva are depicted in sculptures around the base. There are also frescoes in the niches of the sixteen-sided circumference wall.Very popular in Nepal, Avalokiteshvara, having attained Buddhahood, chose to continue as a teacher until such time as all on earth have achieved Bhodi (enlightenment) and escaped the cycle of rebirth. It was he who first took the path of compassion to reach nirvana, a path followed by the adherents of Vajrayana Buddhism. With the aid of his mantra "Om mani padme hum" it is possible, by closing the gates to the six worlds of the Buddhist Wheel of Life, to arrest the cycle of rebirth. The mantra is carved on the prayer wheels placed beside the images of Avalokiteshvara around the base of the stupa.