The War of the Eight Saints (1375–1378) was a war between Pope Gregory XI and a coalition of Italian city-states led by Florence that contributed to the end of the Avignon Papacy.
Causes
The causes of the war were rooted in interrelated issues, Florentine opposition to the expansion of the Papal States in central Italy (which the Avignon Popes had set as a condition for their return), and antipathy toward the Parte Guelfa in Florence. Specifically, Florence feared in the autumn of 1372 that Gregory XI intended to reoccupy a strip of territory near Lunigiana, which Florence had conquered from Bernabò Visconti, and that the Ubaldini might switch from Florentine to Papal allegiance.
Gregory XI also harbored various grievances against Florence for their refusal to aid him directly in his war against the Visconti of Milan. When Gregory XI's war against Milan ended in 1375, many Florentines feared that the pope would turn his military attention toward Tuscany; thus, Florence arranged a nonaggression pact with the English condottiere John Hawkwood, who was Gregory XI's main military commander, at a cost of 130,000 florins, extracted from local clergy, bishops, abbots, monasteries and ecclesiastical institutions, by an eight-member committee appointed by the Signoria of Florence, the Otto dei Preti. Hawkwood also received a 600-florin annual salary for the next five years and a lifetime annual pension of 1,200 florins.
The transalpine mercenaries employed by Gregory XI against Milan, now unemployed, were often a source of friction and conflict in papal towns.
War
Florence formed an alliance with Milan in July 1375, immediately prior to the outbreak of the war, and the prosecution of the war was entirely delegated to an eight-member committee appointed by the Signoria of Florence: the Otto della Guerra.
Florence incited a revolt in the Papal States in 1375. Florentine agents were sent to more than forty cities in the papal states—including Bologna, Perugia, Orvieto and Viterbo—to foment rebellion, many of which had only been re-submitted to papal authority by the efforts of Cardinal Gil Álvarez Carrillo de Albornoz. Humanist Chancellor of Florence Coluccio Salutati disseminated public letters urging the cities to rebel against the "tyrannical" and "corrupt" papal rule, instead urging a return to all'antica Republicanism.
Pope Gregory XI excommunicated all members of the government of Florence and placed the city under interdict on March 31, 1376, banning religious services in Florence and legalizing the arrest and enslavement of Florentines and the confiscation of their property throughout Europe. Initially, rather than attempting to disobey the interdict, Florentines organized extra-ecclesiastical processions (including flagellants) and confraternities, including the re-emergence of groups such as the Fraticelli, who had previously been deemed heretical. The edifice of the Florentine inquisition was destroyed, and the Signoria rolled back legal restrictions on usury and other practices frowned on by the (now defunct) ecclesiastical courts.
However, in October 1377, the government of Florence forced the clergy to resume religious services causing Angelo Ricasoli, Bishop of Florence, and Neri Corsini, Bishop of Fiesole, to flee Florentine territory. The heavy fines and confiscations issued by the Signoria on prelates who left their posts, the "most extensive liquidation of an ecclesiastical patrimony attempted anywhere in Europe before the Reformation," may have been motivated to pay for the increasingly expensive conflict. The total cost of the war for Florence would reach approximately 2.5 million florins.
As a result of Gregory XI's economic sanctions, merchants of the Florentine "diaspora" were hurt economically throughout Europe, particularly the Alberti bankers in Avignon, although the interdict was ignored by many, including Charles V of France.
Hawkwood honored his agreement with the Florentines not to make war in Tuscany, limiting himself to putting down the various rebellions within the papal states; in 1377 Hawkwood abandoned Gregory XI entirely and joined the anti-papal coalition. Gregory XI's other condottieri also limited their activities to Romagna, notably the savage sacking of Cesena in February 1377 in what came to be known as the Cesena Bloodbath. In the spring of 1377, papal mercenaries recaptured Bologna, which up until that point had been a key Florentine ally.