This detailed and meticulous study continues and builds upon recent research into papal crusading policy during the Middle Ages. Despite the survival of a wide range of primary source material on the subject, there has been no comprehensive examination of the crusades in support of the Latin Empire of Constantinople and Frankish Greece during the thirteenth century. Many scholars have considered Byzantine-Western relations between 1095 and 1204, particularly in relation to the impact of crusading, and there have been numerous studies of the course of the Fourth Crusade, which conquered Constantinople and Greece, but although the states of Frankish Greece have been the subject of some good scholarly studies the crusading aftermath of the Fourth Crusade has received less attention. There has been remarkably little study of the papal policies which attempted, and failed, to maintain the Latin Empire of Constantinople set up by the crusaders in 1204. Interestingly, there appears to have been more interest in the period after the Second Council of Lyon in 1274 than in the seventy previous years.

The title of this book might suggest that it focuses on the military aspects of the crusades to Romania – that is, the Latin Empire and Frankish Greece. In fact, there is no detailed discussion of strategy, tactics or military actions. Rather, Nikolaos Chrissis considers papal policy: attempts to link the crusade to Romania to the defence of Jerusalem; efforts to promote the crusade to Romania on the basis that the Byzantine Greeks were schismatics; and diplomatic endeavours to unite the Western and Eastern Churches.

Previous scholars have not considered the military or diplomatic aspects of this subject in detail, often dismissing them as unimportant. This may well be because crusading efforts were an almost unmitigated failure, and often a disaster; yet these were not modest undertakings which should be lightly dismissed. Chrissis traces the evolution of the expedition led by William vi of Montferrat in 1224–5 to protect Thessalonica from Theodore Angelos Doukas Komnenos, ruler of Epiros, who had previously captured a papal legate and the Latin Emperor of Constantinople, Peter of Courtenay. The Montferrat expedition was ‘a substantial mobilization’ (p. 70), accompanied by ‘the granting of indulgences and the commutation of crusading vows’ (p. 72); in its recruitment and funding this was as much a crusade as the Albigensian Crusade which was then underway in the Languedoc. Yet this expedition failed, arriving too late to prevent Theodore from capturing Thessalonica; again, all the papal endeavours to recruit assistance for Latin-held Constantinople could not prevent the Byzantine emperor of Nicaea, Michael viii Palaiologos, from capturing the city in 1261.

Despite the failure of these expeditions, Chrissis demonstrates that they, and the diplomacy that surrounded them, were an integral part of the crusading effort in the thirteenth century, and that it is impossible to comprehend the full extent of crusading in that century without considering these expeditions. He shows that even when there were no plans for a crusade to Jerusalem (for example, in the early 1220s) there were plans in hand for expeditions to Romania. The papacy poured significant resources into recruiting for these crusades, and the papal taxation to finance them aroused considerable antagonism in the West.

Even after 1261 popes still hoped to recover Constantinople for western Christendom, either through force or diplomacy. Chrissis traces the ambitions of Charles i of Anjou, who conquered Naples and Sicily and then cast his eyes towards Constantinople. It was the threat of Charles's military action that drove Michael viii Palaiologus into negotiations with the papacy and the eventual Union of the Latin and Byzantine Churches in 1274. Michael even claimed an interest in the crusade to the Holy Land: Chrissis notes a claim by Marino Sanudo that Michael financed the building of a tower at Acre. The Church Union was annulled by the pro-Angevin pope, Martin iv, in 1281, and it was only the revolt of the Sicilian Vespers in the following year that saved Constantinople from invasion. Chrissis points out that although Michael Palaiologus' role in the conspiracy which led to the Sicilian Vespers is unclear, ‘evidence is overwhelming that he did play a role in it’ (p. 248), thus protecting his own empire. Yet all papal efforts to recover Latin control over Constantinople were unavailing; and by the mid-fourteenth century the papacy would be promoting crusades in support of the Byzantine emperors.

This is a detailed and closely argued study, firmly based on the primary evidence, some of which is from unpublished papal bulls. On the basis of his exhaustive research, Chrissis is able to dissect earlier scholars' theories and show that the crusade in Romania has not only been under-reported but often misinterpreted. Overall this study will be invaluable not only for historians of western crusading policy but also for scholars of the medieval eastern Mediterranean and of Byzantine-Western relations.