Stupas were built as sacred monuments that came to be associated with Buddhism, though the tradition of erecting them may have been pre-Buddhist. They were built because they contained relics of the Buddha such as his bodily remains or objects used by him, which were regarded as sacred. The entire stupa came to be venerated as an emblem of both the Buddha and Buddhism. According to the Buddhist text Ashokavadana, Asoka distributed portions of the Buddha's relics to every important town and ordered the construction of stupas over them. By the second century BCE, several stupas were built at places like Bharhut, Sanchi and Sarnath.

Regarding how they were built, inscriptions found on the railings and pillars of stupas record donations made for building and decorating them. Donations were made by various sections of society. Kings such as the Satavahanas made donations, as did guilds like that of the ivory workers who financed part of one of the gateways at Sanchi. Hundreds of donations were made by women and men who mentioned their names, sometimes adding the name of their place, occupations, and names of relatives. Bhikkhus and bhikkhunis also contributed towards building these monuments.

The structure of the stupa evolved over time. The word stupa is a Sanskrit word meaning a heap. It originated as a simple semi-circular mound of earth, later called anda. Gradually, it evolved into a more complex structure, balancing round and square shapes. Above the anda was the harmika, a balcony-like structure representing the abode of the gods. Arising from the harmika was a mast called the yashti, often surmounted by a chhatri or umbrella. Around the mound was a railing, separating the sacred space from the secular world.

The early stupas at Sanchi and Bharhut were plain except for the stone railings, which resembled a bamboo or wooden fence, and the gateways, which were richly carved and installed at the four cardinal points. Worshippers entered through the eastern gateway and walked around the mound in a clockwise direction keeping the mound on the right, imitating the sun's course through the sky. Later, the mound of the stupas came to be elaborately carved with niches and sculptures as at Amaravati and Shahji-ki-Dheri in Peshawar.