Theravada Buddhist tradition holds that on the full moon day of the lunar month Magha, during the Buddha's own lifetime, 1,250 enlightened monks converged spontaneously at Veluvana, the Bamboo Grove monastery near Rajagaha that King Bimbisara had donated to the Buddhist community, without any of them having been summoned or having arranged the gathering in advance. Tradition identifies four remarkable features that coincided at this single gathering: it fell on the full moon of Magha, all the monks present had been ordained directly by the Buddha himself rather than by any intermediary, all had attained full enlightenment as arahants, and all arrived entirely of their own accord without a prior summons, a combination Theravada tradition treats as unique among gatherings during the Buddha's teaching career.
According to tradition, the Buddha used the occasion to deliver a teaching summarizing the core ethical principles of Buddhist practice, sometimes called the Ovada Patimokkha, addressing the assembled monks on the fundamentals of the monastic discipline and teaching they were to uphold and transmit.
The occasion is remembered as significant for the scale and unusual character of the gathering itself as much as for the specific content of the teaching delivered, standing as an image within Theravada tradition of a fully realized monastic community assembling in complete spontaneous accord.