Which Roman festival in December inspired later gift-giving seasons?

Saturnalia, held around the winter solstice - a week of feasting, gift-giving, gambling in public which was otherwise restricted, and a reversal in which enslaved people were served by their owners and given licence to speak freely. Courts and schools closed, and a mock king was chosen by lot to issue absurd orders.

How much Christmas actually descends from it is more contested than the popular account allows. The gift-giving and the timing line up; but the December date for Christmas has a competing explanation from a calculation nine months after an assumed date for the conception, and the Puritan objection to Christmas as pagan is itself part of how the pagan-origins story spread.

The reversal is the part that interests historians most. Saturnalia is the standard example of a licensed inversion - a society formally suspending its own hierarchy for a few days - and the argument is whether that relieves pressure and reinforces the order, or genuinely destabilises it. Roman writers describe the week with a mixture of enjoyment and irritation, and Pliny the Younger had a soundproofed room built at his villa so he could work through it.