Abstract

This chapter concerns the role of Gregory IX in the conflict between Frederick II and the Lombard League, tracing the roots of this struggle from the time when Gregory was still a cardinal, then exploring the so-called War of the Keys, the re-emergence of the Negotium Lombardie in the 1230s, and the descent into armed conflict at the end of Gregory's pontificate. It is argued that in contrast to the previous struggle with Barbarossa, heresy and penitential warfare came to play a central part in the political conflicts between Gregory and Frederick, which ultimately took on all the trappings of a full crusade.

Keywords: Frederick II, Lombard League, heresy, crusade, Barbarossa

Among the most striking differences between the two major conflicts that involved the papacy, the Lombard cities and the empire in the twelfth and thirteenth centuries were surely the role that papal involvement, heresy and crusades played within them. The first conflict, which embroiled the Lombard League, Frederick Barbarossa and Alexander III from the papal schism of 1159 to the Peace of Constance of 1183, started before the creation of the League, which the papacy fully backed against Barbarossa. Yet the confrontation between pope and emperor finished at the Peace of Venice of 1177 – before that between Barbarossa and the League – and the papacy only played a very light supervisory role in the subsequent truce and negotiations that led to the Peace of Constance. Moreover, that first conflict was not tied to Alexander's appeals for the Holy Land (the conflict took place between the second and the third crusade) or his anti-heretical activity. Alexander proclaimed that the League was defending the libertas Ecclesie and was inspired by the Holy Spirit, and he threatened and punished defectors from the League with interdicts and excommunications. Yet he never equated Barbarossa's position to that of a heretic, and the conflict did not take on crusading features. In contrast, roughly half a century after the Peace of Constance, the papacy provided arbitration in the struggle between Frederick II and the League (which primary sources called the Negotium Lombardie) for more than ten years after it started in 1226. That involved first, and very briefly, the participation of Honorius III, but mostly that of Gregory IX. Within that period the League sided with the papacy during the crisis that led to the so-called War of the Keys in 1227–1230.