What should we make of Pope Pius ii’s Commentarii? Pius dictated this substantial text between the summer of 1462 and the spring of 1464, and the paper codex, Vaticano Reginense Latino 1995, contains many subsequent changes made by the pope himself. In other words, at the height of a busy and tumultuous reign, Pius set aside valuable time – ‘snatched from sleep’ as he put it – to establish his own account of what he had so far done as pope and why he did it. Twelve books were completed, the thirteenth consisting of a fragment which was omitted from the fine parchment copy finished for the pope by Giovanni Gobellino in June 1464. Of course the Commentaries are tendentious, but they have proved irresistible to many historians of Pius' reign. In the first place, they constitute a unique source: a set of papal memoirs written during the heat of events – ‘a view from within the eye of the storm’, as Emily O'Brien puts it – as Pius struggled to bring about the central goal of his reign, a crusade against the Turks. And in the second place, they are consistently elegant, incisive and witty. It is as if Gore Vidal had become president of the United States and written his memoirs while still in the White House. How Vidal would have enjoyed Pius' putdown of Jacopo Tebaldi, ‘small of stature, but smaller in mind’.

Pius' reason for writing is unknown but it is far from being mysterious. He had always written compulsively, easily and fluently, and he was fascinated by the exercise of power. It would have been anomalous if he had failed to offer his own interpretation of events, even if the exact nature of his intended audience cannot now be pinpointed. O'Brien wastes no time on this question. Her theme is the image that Pius sought to create in the Commentaries and its relationship to two other tranches of evidence. One tranche is of course the substantial seam of contemporary sources that illuminate the pope's reign, which scholars like Barbara Balbi and Riccardo Fubini have mined so effectively. The other is the collection of writings by Pius before he was elected in 1458. A group of these, the Dialogus, the Pentalogus and the Germania, have appeared in up-to-date editions in recent years, though for the crucial letters we remain dependent on Rudolf Wolkan's edition, a fine example of German scholarship but now a hundred years old.

O'Brien divides her book into two sections, each comprising three chapters. In the first half she addresses the problems faced by the restored papal monarchy, notably the ongoing challenge of conciliarism, the resistance mounted by the secular powers to any attempt to recover past prerogatives, and the achievement of stability in central Italy. O'Brien sees this cluster of threats as amounting to a crisis, which I believe is too dramatic. By definition crises are either overcome or are themselves surmounted, and the Renaissance Curia survived through a mixture of accommodation and the adroit management of turbulence that never fully subsided. The retreat of papal authority in the face of secular power, and the problems posed by Italian politics, were certainly unending; and O'Brien is correct to emphasise that all the popes from Eugenius iv onwards were also deeply concerned about a revival of conciliarism. Pius ii’s own bull prohibiting appeals to a future general council, Execrabilis (1460), was far from being the death knell of the movement. O'Brien affirms that it was never included in the chancery registers and its circulation was heavily restricted.

In the second half of her book O'Brien focuses on the Commentaries. Her argument is that they ‘constitute a far more ambitious and aggressive work of defence than has yet been realized’. With forensic skill she demonstrates how adroitly, through a mixture of selective omission and misrepresentation, Pius engaged in the dual project of airbrushing his own dubious past and placing the best possible interpretation on his deeds as pope. The man was without doubt a master of spin. The threat posed by conciliarism even after Basle's dissolution is expunged so thoroughly from book i that when Pius himself has to deal with it, the reader wonders why it has suddenly become a problem. Pius succeeds in depicting himself as a zealous reformer, an impartial and efficient administrator of the Church and its lands, the best judge not just of Christendom's shared interests, but of what would be best for each of its states (in particular the Italian ones). But even Pius could not work miracles, and O'Brien shows that while the pope succeeds in casting numerous individual episodes in a favourable light, he could not conceal the reality: that the overall record of his pontificate, even before the debacle of his failed crusade, was unimpressive.

O'Brien's book is not without its faults. There are errors, such as the misdating of the preaching of the First Crusade to 1098 and the claim that no fewer than a hundred beautiful Scottish women offered sexual favours to the young Piccolomini in 1435 (as opposed to the two later recorded by Pius). More importantly, the structure adopted entails a large amount of repetition, which is not assisted by O'Brien's tendency towards prolixity. I do not think that she fully grasps the relations between Eugenius iv and the Council of Basle, which is understandable given their complexity. She has been too heavily influenced by recent Italian scholarship which has ‒ unsurprisingly ‒ emphasised the pope's peninsular policies. This in turn leads her to adopt an over-politicised perspective on his crusade plans. The fact is that in the mid-fifteenth century prioritising the promotion of a crusade was just about the least effective way to defend the papal office against its many opponents and threats: it was an invitation to over-exposure, failure and a barrage of criticism. It is regrettable that she was not able to make use of Benjamin Weber's Lutter contre les Turcs: les formes nouvelles de la croisade pontificale au XVe siècle (2013). Weber uses the massive documentary output of 1458–64 to place Pius' crusade programme firmly in context, making it possible for the first time to compare what he did with the actions of popes both before and after. But for all its demerits, O'Brien's book remain an interesting and significant study of the reign and the wonderfully appealing but misleading record that Pius himself bequeathed to posterity.