How were the Buddha's words kept for centuries before anyone wrote them down?

They were memorised. According to Buddhist tradition, soon after the Buddha's death a council recited his teachings: Ananda recited the discourses, the Sutta Pitaka, and Upali the monastic rules, the Vinaya Pitaka. The monks present accepted the recitations, and from then on the Sangha, the community of monks, preserved the teachings orally. The word for such a council, saṅgīti, literally means "reciting together".

Historians agree on the oral part but not the details. Scholars point to the texts themselves: they were meant to be memorised and recited, there is no evidence that writing was used to preserve them, and their style (repetition, standard phrases, numbered lists) is the style of spoken literature. The texts are believed to have been passed down by lineages of monks called bhāṇaka, who specialised in memorising and reciting particular collections, until they were eventually written down: the Theravada tradition's own canon was first written down in Sri Lanka, no earlier than 29–17 BC.

Could memory really be that accurate? Alexander Wynne argues that the accuracy of oral transmission should not be underestimated, because the Buddhist community included Brahmins who knew the Vedic system had handed down a mass of difficult texts word for word for over a thousand years. Not everyone agrees on how fixed the texts were: other scholars think they could have been performed in more improvisational ways using lists and formulas.

The tradition lives on. Lay people usually know a few short texts by heart and recite them regularly, and a Burmese monk named Vicittasara learned the entire Canon by heart for the Sixth Council.