The correct answer is Bas-relief.

The Great Stupa of Amaravati, located in the Lower Godavari region of Andhra Pradesh, India, is renowned for its extensive use of bas-relief sculptures. These sculptures, carved in low relief, adorned the walls of the stupa, depicting scenes from the life of Buddha, Jataka tales, and other Buddhist narratives. Unlike high-relief sculptures (alto-relievo) that project significantly from the background, bas-reliefs are shallowly carved, creating a subtle yet detailed narrative across the stupa's surface. The choice of bas-relief was particularly effective for covering vast areas of the stupa's circumambulatory pathway, allowing for a continuous and immersive storytelling experience for pilgrims. The technique allowed for a large number of scenes to be displayed within the limited space available on the stupa's walls. Sunken relief and freestanding sculptures are not characteristic of the Amaravati style. The shallow depth of bas-relief offered a visually appealing and narratively rich decorative element, while also being structurally sound and suitable for the curved surfaces of the stupa.