Assertion: Stupas are venerated as an emblem of both the Buddha and Buddhism.
Reason: The relics of the Buddha such as his bodily remains or objects used by him were buried in stupas.

Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

The tradition of constructing stupas might have existed prior to Buddhism, but they became closely associated with the religion. These stupas were revered due to their containment of sacred relics, making them symbols of both the Buddha and Buddhism. According to the Buddhist text, Ashokavadana, Emperor Asoka distributed portions of the Buddha's relics to significant towns and directed the construction of stupas over them. By the second century BCE, several stupas, such as those found at Bharhut, Sanchi, and Sarnath, had been erected.