Final answer:
The railing atop the Great Stupa symbolizes a boundary between the earthly realm and the cosmos, representing the universe and the path to enlightenment in Buddhism.
Step-by-step explanation:
The railing at the top of the dome, the Great Stupa, serves symbolically as a representation of the cosmos and a divine connection. The stupa itself is a significant structure in Buddhism, embodying the Buddhist path to enlightenment. The circular shape of the dome represents the idea of the universe and infinite space, while the railing, often adorned with intricate patterns and symbols, embodies a boundary between the earthly world and the heavens. In many cases, such architectural elements also underscore the power and wealth of the city or kingdom that built the stupa, thereby linking the earthly realm with cosmic order and religious significance.