Suffer the little children ...

In 1870, ten years after the Unification of Italy, Italian troops blew a hole in the Aurelian wall that surrounds Rome and seized the holy city from Pope Pius IX. While the rest of Italy had been adapting itself to secular, modern Europe, the Pope had held onto the last vestiges of papal territory against the combined forces of Count Cavour, Garibaldi and Napoleon III. To nationalists and liberal Catholics alike he had come to be seen as a medieval relic wielding temporal powers that were an anachronism. Besides, a united Italy without Rome was a body politic missing its heart.

But the social anthropologist David Kertzer shows that what really did for Pius IX was the Mortara case. This cause celebre turned an obscure Italian-Jewish family into unwitting agents in the final, crucial stage of the Risorgimento. Using contemporary accounts and personal testaments, Kertzer resurrects this now-forgotten scandal to provide a compelling "history-from-below" of the events leading up to the formation of the Italian state. In so doing, he makes evident the devastating impact of warring religious and secular beliefs on the lives of a single family.

The story of the Mortaras, which has never before been recorded in full, has all the drama of a political thriller. Kertzer starts his account in the dead of night in Bologna, in 1858, when a squad of papal police entered the Jewish ghetto and forced their way into the home of the Mortaras, in search of their six-year-old son, Edgardo. A few years before, the Mortaras had kept a Catholic nursemaid who had cared for the boy when he was sick. Fearing he might die, she had secretly baptised him and later confided her worries to a neighbour. Somehow, and despite Kertzer's efforts no one really knows how, the Holy Inquisitor found out and, applying the tenets of canon law, sent his henchmen to wrest this "Christian" child from Jewish custody. By making the sign of the cross, sprinkling water over her charge's head and intoning "I baptise you in the Name of the Father, the Son, and the Holy Ghost," this 14-year-old servant girl had triggered an international scandal.

Bologna's free-thinking intellectual elite was outraged by the Inquisitor's actions. Italian Jews were mobilised and the story of the child snatched from his distraught parents' arms spread quickly, pulling at Europe's heartstrings. French playwrights transcribed it for the theatre, American Jews staged mass protests, and Napoleon was delighted with this effective propaganda tool. Edgardo's story was used by opportunistic Nationalists to chip away at papal authority, and gain a foothold on Rome.

Meanwhile, the Church and the Jewish community were constructing contradictory versions of Edgardo's abduction. Confined to a Roman convent, he was described by his keepers as having undergone a miraculous conversion, whereas his mother told journalists of a confused and bewildered child whose recitation of Jewish prayers was continually interrupted by priests demanding Hail Marys. The Church invited comparisons with the infant Jesus: Edgardo, they claimed, was in the house of his Father - how could he be returned to the Jews? Pius IX refused international pleas to set him free, unless his family converted. Edgardo, as well as serving political ends, became a sacred cause.

Kertzer is even-handed in his treatment of the opposing, fanatically held systems of belief that overwhelmed the Mortaras. He also gives a grim account of the Italian's oppression of Jews. Forced to take communion every Sunday, and to wear badges on leaving their ghettos, Jews were incredulous at this latest act of persecution. The Mortaras' campaign - although it failed to reunite the family - managed to consolidate the international Jewish community, and gained them high-profile support. Too late, the Pope recognised the consequences of his intransigence. When Edgardo reached 15, and had become a devout seminarian, he received the following letter from the Holy Father:

"You are very dear to me, my little son, for I acquired you for Jesus Christ at a high price. So it is. I paid dearly for your ransom. Your case set off a world-wide storm against me and the apostolic See."

Edgardo remained forever estranged from his family.

Given the growth of secessionist politics in contemporary Italy, Kertzer's story is of immediate relevance, as well as being alive to the tragic implications for its protagonists. In 1878, the widowedMarianna Mortara visited her sonin Perpignan where he was preaching. It was the first time she had seen him in 20 years. "It was a poignant reunion, for Edgardo felt great affection for his mother. But try as he might to turn her onto the path of eternal blessing and happiness, he could not get her to agree to enter the Catechumens and convert." As for Edgardo, after a lifetime of itinerant proselytising he died in a Belgian monastery, aged 88, on 11 March 1940, a month before German soldiers invaded the village and began their rout of its Jews.