As the primary symbol of Buddhism - and its holy of holies - the stupa, a burial mound that takes many forms, was not known to Buddhism itself until the time of the 3rd century bce Indian emperor Ashoka who is credited with the acceptance and spread of Buddhism.
The original meaning of the word stupa was topknot, and the stupas resembled Gautama Buddha's own topknot, as artists and architects believed it to have been.