The Great Stupa, originally built in brick by Ashoka and later encased in stone, is located at:

The correct option is Sanchi.

Explanation

The Stupa is a hemispherical structure containing Buddhist relics, serving as a focal point for worship and meditation. The architectural evolution of the stupa, particularly the transition from brick to stone, marks a significant phase in ancient Indian art history.

Detailed Analysis:

• Sanchi (Option a): The Great Stupa (Stupa No. 1) at Sanchi is the correct answer. It was originally commissioned by Emperor Ashoka in the 3rd century BCE as a simple brick structure. During the subsequent Shunga period (mid-2nd century BCE), the stupa was expanded to nearly twice its original size and encased in stone slabs. This period also saw the addition of the stone balustrade (vedika) and the flattening of the dome near the top to accommodate the harmika and chhatra.
• Bharhut (Option b): The stupa at Bharhut was constructed primarily during the Shunga period. While it is famous for its narrative sculptural reliefs, the specific history of an Ashokan brick original being encased in stone is the defining characteristic of the Great Stupa at Sanchi.
• Amaravati (Option c): The Great Stupa at Amaravati is associated with the Satavahana period (2nd century BCE - 3rd century CE). It is renowned for its intricate carvings on white limestone (often called Amaravati marble) but does not fit the description of the Ashokan brick core encased in stone in the same context as Sanchi.
• Bairat (Option d): Bairat (Viratnagar) contains the remains of a circular Buddhist shrine (Chaitya-griha) dating to the Mauryan period, but it is not the site of the "Great Stupa" described in the question.

Key Takeaway:

The Great Stupa at Sanchi is a classic example of the architectural transition from Mauryan brickwork to Post-Mauryan (Shunga) stone masonry.