Why a council was called
The Vinaya's Chapter on the First Council begins with a shock. Soon after the Buddha's death, an elderly monk named Subhadda told grieving monks not to mourn: now, he said, they could do as they liked, with no one to tell them what was proper.
Mahākassapa, the most senior disciple, heard this and proposed that the community recite the teaching and the discipline together, before false teaching could grow. Five hundred monks, all said to be fully awakened, gathered at Rājagaha for the rainy season.
Reciting the teaching
Upāli, the expert in monastic discipline, was questioned on each rule: where it was laid down, about whom, and why. Then Ānanda, the Buddha's attendant for many years, was questioned on the discourses, each of which traditionally begins 'Thus have I heard'.
Ānanda reported that the Buddha had said the minor rules could be dropped after his death, but he had not asked which rules were minor. Unable to agree, the council decided to keep every rule. Ānanda was also taken to task for several lapses, which he accepted for the sake of harmony.
Afterwards a monk named Purāṇa, who had not attended, said politely that the recitation was well done, but he would remember the teaching as he himself had heard it from the Buddha.
Why it matters
It symbolizes the Buddhist concern with maintaining teachings after the death of the Buddha.
History and tradition
What historians can say
Most historians doubt that the council happened as described. The account was written by later monks to show that their scriptures went back to the Buddha, and versions from different schools disagree in details. What it does reflect is real: the teachings were preserved by group recitation, in a structured oral tradition, for centuries before they were written down.
What Buddhist tradition remembers
Tradition holds that Ānanda, still not fully awakened, reached awakening on the night before the council opened, in the moment of lying down, so that he could take his place. Later tradition adds that King Ajātasattu sponsored the gathering.