Honorable men, as they were called in the golden age of chivalry, were rich enough to outfit a squadron of knights and brutal enough to lead them into battle, often culminating in the killing and plundering of civilian populations. The code of chivalry defined honor in ways that are familiar to people today — as honesty, loyalty, courage — and in ways that are not. It was honorable, for example, to show mercy to a defeated enemy, but only if the enemy was a social equal.

There was no dishonor in slaughtering commoners.

Maurice H. Keen, a historian who presented that unvarnished view of the medieval nobility in his book “Chivalry,” was one of a small group of scholars in the 1980s who re-examined the record of the chivalric knights, long portrayed in romantic literature as do-gooders, and who found it — with all due respect to Thomas Malory and Walter Scott — incomplete.

There were many do-gooders and brave fellows, no doubt. And the chivalric code did moderate and civilize men’s behavior, especially toward women of equal status. But Mr. Keen, who died on Sept. 11, argued that chivalry was mainly a “cult of martial virtues” for men and about men, charting a path to glory, honor and wealth. From about 1150 to 1500, he wrote, obeying its code was the only way for aristocrats to move higher on the social ladder and the only way for commoners to reach the first rung....