In a moment of candor and humility, the late Pope Paul VI admitted that the papacy itself - and specifically the doctrine of papal infallibility, fought for so relentlessly by his predecessor, Pius IX - is one of the greatest obstacles to Christian reunion. How that doctrine went from being a minority opinion at the beginning of the nineteenth century to a solemnly defined dogma at the First Vatican Council in 1870 makes for the fascinating story of personality conflicts, papal politics, and doctrinal transformations that the Swiss historian August Berhard Hasler recounts in this controversial book. At center stage is the redoubtable Pius IX, for whom the achievement of a binding conciliar definition of papal infallibility became a crusade, if not an obsession. Hasler details how he bullied and coerced opponents of the definition and hounded doubters after the doctrine was proclaimed by having their works placed on the Index of Forbidden Books, Did the pope's epilepsy influence his behavior? Did the pressures ha and his allies exerted on the waverers among the bishops render the Council unfree and its decisions of questionable validity? These are the kinds of questions Father Hasler raises in his thought-provoking and ultimately constructive effort to reopen debate on the major issue that still divides Christians and makes headlines more than a century after the doctrine was solemnly proclaimed.