King Arthur and the Knights of the Round Table are very well known stories. Arthur was popularized in the novel History of the Kings of Britain by Geoffrey of Monmouth, but the Round Table was first mentioned in 1155 in Roman de Brut. The Round Table was created by Arthur's father, who gave it to King Leodegrance, Guinevere's father. After she married Arthur, they were given the table as her dowry. Arthur sat his knights at the table to prevent fighting over seating order.

The Knights of the Round Table were members of the military and were Arthur's highest order of chivalry. They followed a strict code of honor which was based upon "patience, humility, and meekness." Such standards included to be religious, to never harm other people, to defend and, if needed, sacrifice one's self for one's country, to be merciful and honorable, to fight for and protect gentlewomen, to keep one's word, et cetera. Basically, they were to follow typical honorable and religious conduct.

The number of knights varies, apparently because there were lesser orders of chivalry established afterwards, including the Queen's Knights.

Sources: and