This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Buddhism arises in the Ganges plain in the fifth century BCE, in the region of what are now the Indian states of Bihar and Uttar Pradesh. The Buddha's own teaching career unfolds there across several decades: a first sermon traditionally placed at Sarnath near Varanasi, itinerant teaching through the kingdoms of Magadha and Kosala, and the formation of the earliest monastic community, the sangha, that would carry the teaching forward after him.
No single dramatic conversion carries this event. It is the Buddha's own lifetime of teaching, gathering disciples one at a time into a durable community with its own rule and its own memory of what he said, that turns a single teacher's career into a tradition capable of outliving him. What changes for Buddhism's spread is everything that follows from it: a monastic order exists to carry the teaching onward once the Buddha himself is gone, into Sri Lanka, into Central Asia, and eventually across the whole of Asia.
The dating is debated within a range near the fifth century BCE rather than fixed to a single year, and no dedicated Ganges plain place exists in this atlas's catalog of locations, so the event is anchored to India, the nearest real place on record, an approximation named here rather than rounded over in silence.