The title of James Carroll's groundbreaking work on the complicity that the Roman Catholic Church has in the persecution of the Jews - Constantine's Sword - summons up the well-known story not only of the conversion of an emperor, and thus, the Western world, to Christianity, but the conversion of a symbol not central to pre-Constantinian Christian faith into the single defining symbol of the religion from that age on. As Carroll puts it, quoting Eusebius:

'Constantine saw with his own eyes the trophy of a cross of light in the heavens, above the sun, and bearing the inscription "CONQUER BY THIS.' The story goes on to say that Constantine then assembled his army. . .and gave them the new standard to carry into battle. 'Now it was made in the following manner. A long spear, overlaid with gold, formed the figure of the cross by means of a transverse bar laid over it.'

By this point in the book, Carroll has already traced the birth of Christian thought in the culture of Judaism and its thoroughly Judaic origins, as well as the growth of separation between the young Christian movement and the rabbinic Judaism that developed alongside of it. Carroll expresses his understanding of the creation of a spear-cross as the standard of a conquering Christianity: "When the death of Jesus - rendered literally, in all its violence, as opposed to metaphorically or theologically - replaced the life of Jesus and the new life of Resurrection at the heart of the Christian imagination, the balance shifted decisively against the Jews. This was so because sole responsibility for that now pivotal death had long since been laid at their feet." Carroll's story is that of a people branded as "the deicide" by the Church, in alternate times tolerated with slight humiliation directed towards them, at others openly attacked and murdered with official Church indifference or even provocation. He follows the cross through history, as well as the single city of Trier as one part of a Western odyssey through the Christian oppression of the Jews.

This city is the site of Constantine's palace, now a Lutheran church; the location of the prized relic of Christ's "Seamless Robe", long used as a Church testament to the inferiority of Isaiah and other Jewish texts as merely "predicting" the superior religon of Christianity, and displayed proudly to Nazi visitors in 1933; the place of "the incident at Trier", related by Jewish historians, where Christian Crusaders, stirred to fervor by Peter the Hermit and Pope Urban II, demanded payment from the Jewish community, and then destroyed the synagogue and Torah, and tortured and killed the Jewish occupants of the city; the home of both the Jewish family that produced Karl Marx and the Gentile family that produced SS officer Klaus Barbie; and finally, the place where the author himself viewed the Seamless Robe in 1959, a little over a decade after the close of World War II, in which the systematic murder of six million Jews seemed to completely displace all the history of Western civilization. It is Carroll's intent not to blame the Church, but, as a Catholic, to acknowledge its wrongdoing - and provide some context in which the Holocaust, which will never be understandable, might be recognized at least as connected to the anti-Jewish rhetoric of the Church itself. He uses this study of the eternal connection with and the fear that the Church has consistently had for those who challenge its hegemony - the Jews, refusing to convert and thus undermining the claim that the Jewish covenant was replaced by that of Christ, being the most egregious "offenders" - to advance a new idea for a Vatican Council that would not only recognize the sins of the Church in the past but foster a new understanding of the role of the Church and its leadership in a modern and pluralist world.

Carroll's story begins in the present day, relating the massive controversy that has raged between the Catholic Church and much of the worldwide Jewish community when the Polish Christian community surrounding Auschwitz planted a large cross in the ground of that infamous site, in reactionary response to Jewish protests over the presence of a convent of Carmelite nuns in one of the camp's buildings. The cross was planted by the "starvation bunker" to recognize the death of the recently-canonized Father Maximilian Kolbe inside this building during World War II - and who was also the publisher of an openly and angrily antisemitic Catholic journal in the years before. Carroll approaches this problem with the understanding that Christians, in many ways, do not "understand" what it is like for Jews to see the place where they were killed for their blood alone invaded by a symbol underneath which many of them suffered, or to see it called "the Golgotha of the modern world" by Pope John Paul II when the crime of Jesus's death was so long placed on their heads as a people - or to see Kolbe and the convert Edith Stein canonized as martyrs, when the latter died among millions of Jews for merely being born a Jew, not for practicing as a Catholic. Constantine's Sword exhaustively presents the entire history that leads up to this confrontation over the Shoah, and asks the question: if it was not the Church that perpetrated such a horror, then how could it have allowed it to be so easy?