Even now, to most people, the Middle Ages are a sort of historical black hole into which civilization vanishes with the fall of Rome, to be recovered only after a thousand stagnant years by the Renaissance. Yet the medieval culture was wonderfully creative. Medieval people invented windmills and water mills and tide mills, made clocks and horseshoes, devised ways to plow the heavy soils of the north and to mine the unreachable treasures beneath the earth. In the course of a thousand years they also invented a new society, based on the inherent worth and, in a rudimentary way, on the equality of individuals.

Frances Gies' new book, "The Knight in History," chronicles the rise of a crucial part of this society: the knightly profession. Like all the great medieval inventions, the idea of knighthood was a response to the pressures of necessity. What to do with boisterous and bellicose young men is a universal social problem, perhaps based in the genes: Even now, with so many more opportunities available, young men still spend a good deal of their time in combat, real or symbolic. We turn them into football players; the Middle Ages made them into knights.

The ideal of the knight was born in the efforts of the church to control the savage feuds and private wars that constituted routine political practice in the 9th and 10th centuries. The method was a fairly common strategy: to make the disrupters of the peace into the peacekeepers. Knights were given the sacred duty of enforcing the Truce of God, the church's ban on murder and mayhem of all kinds from sundown on Wednesday to sunrise on Monday; that they defended this order almost always against other knights seems to have offered no one any philosophical difficulty.

Unsurprisingly, the murder and mayhem scarcely diminished; in the 11th century the church found it necessary to send as many of these men as possible abroad in the Crusades. The rising coherence and competence of the knightly profession made the Crusades not only possible but surprisingly successful.

In the Crusades, the faith that had been midwife to the original knight still dominated his thoughts and deeds. But the knight's power and his actions were temporal, not spiritual; even disguised as a monk, as a Knight Templar, he soon became utterly a man of this world.

There was now more in this world to enjoy. After centuries of disorder and misery, things were getting better for most Europeans by the end of the 11th century. In Southern France, seat of a culture sophisticated in the worldly arts, a more subtle and elegant way of life appeared, and skill at writing verses became as much a knightly accomplishment as battery with swords. The troubadours of Provence were knights; their verse is steeped in the values and symbolic organization of their way of life. In an extraordinary chapter on this little-known body of work, sophisticated and lively, Geis reproduces some marvelous pieces.

"Ah, Bels Senher, Maent, at last

I ask naught of you,

Save that I have such hunger for

This phantom

As I've for you, such flame-lap,

And yet I'd rather

Ask of you than hold another . . ."

The knights belonged to the world, not to God.

Gies makes splendid use of literary sources, like the "Chronicle de Bertrand du Guesclin," to open up before us the practical experience of the medieval knight. Most of these chronicles are virtually useless as narrative history, but as windows into their time they are magnificent little Bruegels for detail and color, and Gies gets the most from them. No parade of statistics or analysis of demographics could have the immediacy of scenes like the one in which du Guesclin and his men sneak into an enemy castle disguised as peasants bringing firewood, their swords hidden under long skirts and their beards under sunbonnets.

Mention of the Middle Ages always conjures up the picture of a knight in armor. This detailed look, focusing as it often does on individual men, divests the knight of much of the cliche' attendant on him, and shows him in a new and more interesting light, whether Roland or Galahad.