Received wisdom has it that Buddhism disappeared from India, the land of its birth, between the thirteenth and fourteenth centuries, long forgotten until British colonial scholars re-discovered it in the early 1800s. Its full-fledged revival, so the story goes, only occurred in 1956, when the Indian civil rights pioneer Dr. B.R. Ambedkar converted to Buddhism along with half a million of his Dalit (formerly "untouchable") followers. This, however,...