The melody is graceful, a bit sad, with a vaguely Middle Eastern flavor in some of its cadences. The words (in medieval French) could hardly be more graphic: "Those vile, dirty, stinking criminals are slaughtering the simple people." The song is one highlight among many in the Folger Consort's program, "Troubled Times," which has its final performance tonight at the Folger Shakespeare Library.

The poet and composer was Thibaut, count of Champagne and king of Navarre, and he was writing about civil war: the Albigensian Crusade, which pitted Christian against Christian, northern against southern France. After a quarter-century, the crusade ended with the destruction of the courtly Provenc,al society that had been the cradle of modern, vernacular European poetry. It was a confusing experience -- not unlike our own in Vietnam -- for the knights who subscribed theoretically to a lofty code of chivalric morality and who had been accustomed to the more clear-cut crusades of Christian against Muslim, where the enemy was easier to recognize. How can we tell the true believers from the heretics, one soldier reportedly asked Simon de Montfort, leader of one expedition, and Montfort's reply is one of history's most chilling lines: "Kill them all; God will recognize His own."

Another royal poet, Richard the Lion-Hearted, captured and held for ransom, writes from prison: "Dead men and prisoners have no family or friends." A monk writes about his visit to heaven where God agrees with him that "singing and laughter" are better than such quarrels. In an anonymous song, Fair Doette learns of her lover's death in combat far away.

The second half of the program was devoted to music from another religious war, the 17th-century battle of Cavaliers and Roundheads in England. Some of the music was lovely, but it seldom reached the expressive power of the medieval material; the Cavalier poets and composers were trained to be charming above all, and their charm was not really equal to the horror of the war. But the music from both periods was splendidly performed by the Consort, aided by three superb guest artists: soprano Johana Arnold, tenor Peter Becker and Tina Chancey playing stringed instruments.