A stupa is a dome-shaped structure that serves as a reliquary and memorial to the Buddha and other Buddhist worthies. Originally these structures were hemispherical mounds of stone or brick, surrounded by a low fence. In East Asia, the superstructure above the dome became taller and more ornate, eventually evolving into the pagoda form. Among Tibetans, circumambulation of stupas is a popular practice for both monastics and laity.