James Carroll won the National Book Award for his "An American Requiem," the highly personal story of his taut relationship with his father, an Air Force general, while Carroll was marching in the protests against the Vietnam War. Carroll's gift is his ability to weave a personal account into the portrait of an era. In "Constantine's Sword," he stretches these talents onto an enormously larger canvas. Once again combining candid autobiography with historical narrative, he rehearses the sordid saga of 2,000 years of Christian anti-Judaism as it has unfolded under the sign of the cross.

"Constantine's Sword" is a highly risky enterprise, and though Carroll sways occasionally, he manages to traverse the 616-page high wire without toppling into the abyss of generalized guilt, and without ever losing the reader's rapt attention. It is the stunning achievement of a fine writer.

When Carroll visited Auschwitz some years ago, he knew that the wooden cross his fellow Catholics had erected there had already sparked fierce debate. Many Jews saw it as a desecration. Some Christians agreed with them, but others thought it appropriate--after all, some Christians had died at the death camp. As he stood at that controversial cross, Carroll was thrust into a searching and painful inquiry. Somehow everything that had gone into the making of hiss life was called into question. How could the symbol he loved, the cross, be such a powerful reminder of God's love and at the same time be for so many Jews a reminder of the hatred and oppression that had prepared the ground for the final solution?

Carroll's visit made him face questions about a centuries-old record of Christian anti-Semitism, and therefore the deepest foundations of his own faith. He knew that if he discovered--as some have contended--that there is something essentially anti-Jewish about Christianity, he could have nothing more to do with the faith he had been raised in, still observed, and even once served as a priest. He knew it would be a hazardous undertaking.

But Carroll also realized that, in the words of theologian Karl Rahner (which he cites on the first page), one must not only have "the courage to ask questions" but to ask them "with the mind and heart one actually has, and not with the mind and heart one is supposed to have." Carroll's faithful adherence to Rahner's precept is what saves him from tedious breast-beating or straining the reader with defensiveness. Instead, he ventures forthrightly on what was both an agonizing inner journey and a bold march through a tortuous history. The volume he has produced will surely shape the contours of the Jewish-Christian dialogue for years to come.

But it will do more than that. Carroll's brutal honesty--his commitment to think and write with the mind and heart he actually has--can't fail to push every reader into an equally disturbing interior exploration. Carroll's research takes us from Auschwitz back to the cross on which the Romans executed an obscure Galilean rabbi; to the Emperor Constantine's commandeering of the cross as his imperial escutcheon; to the cross on the crusaders' gory shields; to the cross thrust into the eyes of the victims writhing in the inquisition's flames; to the Jew-hatred of the modern French journal La Croix; and then, with numbing momentum, back to Hitler and Auschwitz.

The expedition is anything but comfortable. But unlike some other treatments of this ugly legacy, Carroll never wallows in his own guilt and is not even particularly interested in forgiveness. His question is much more urgent: Can an honest unearthing of the past help avoid a repetition of this shameful chronicle in the future, and if so, how?

For Carroll, the answer is to be found in how we cope with memory, especially with memories we wish we could forget. We hear much about what Pope Pius XII might have done, or should have done, to oppose the Shoah. Carroll thoroughly exposes what he calls the church's "self-exonerating" statements on this troublesome period. But he probes even deeper. A "far graver issue arises, "he says, "than the silence of one man. The question rather becomes, how did a succession of popes prepare the way for the 'silence' of an entire civilization?" And did those popes reflect a pervasive hostility to Jews that infected the entire church?

Beginning at the beginning, Carroll reminds us of Jesus' lifelong Jewishness. But he points out how quickly the early Christians' efforts to truckle to Rome caused them to mute Jesus' fidelity to his Jewish religion--even in the gospels themselves.

Jesus, of course, knew about crosses. They were the hangman's nooses of his day, and living under the leaden heel of the legions, he saw them frequently and must have contemplated the experience: The Romans first tortured to death anyone, like him, who dared question their authority, then left them to rot as an example.