Final answer:
King Arthur typically required a marvel or an adventure to be presented before he would sit down to a feast, as a symbol of chivalry and heroism at the Round Table.
Step-by-step explanation:
The question 'What does Arthur (the king) require before he will sit down at any feast?' refers to a tradition or condition that King Arthur might have required before partaking in a feast. While the specific details of this practice can vary across different Arthurian legends and stories, commonly in Arthurian lore, King Arthur would wait for a marvel or an adventure to present itself before he would commence a meal at the Round Table. This tradition is meant to underscore the focus on chivalry and heroics among the knights of the Round Table. For example, in some stories, it is said that Arthur would not eat until he had heard a tale of great valor or had been presented with a quest upon which he or his knights could embark.