|Pope Gregory XI arriving in Rome in 1377|
Fresco by Giorgio Vasari
Understandably, the Italian city-states objected to this; if Gregory wanted more land, he was going to have to take it by force. Gregory was fine with that option. He was fighting a battle with Milan, and when that ended in 1375, he had the opportunity to send his army against Florence, which held lands that would have been ideal for Gregory. Thus started the "War of Eight Saints."
The head of Gregory's mercenary army was an Englishman, John Hawkwood. Florence decided they could "buy off" Hawkwood. They offered him (and his army) 130,000 florins to sign a one-year nonaggression pact with Florence. For Hawkwood himself, they offered an annual payment of 600 florins in a five-year contract and a lifetime annual pension of 1200 florins! Hawkwood kept his involvement to the Papal States themselves, avoiding conflict with Florentine territory. Gregory had to use other forces to attack key areas in Italy.
Who were the "Eight Saints" of the war? Their names aren't agreed upon, and they weren't saints. Gregory excommunicated Florence for its opposition, using the phrase otto dei preti ["eight priests"] to refer to specific men whose acts prompted the excommunication.* These eight would have been one (or both) of two groups of eight men: one was appointed to come up with the means of buying off Hawkwood (these men also forced a loan on the clergy of Florence to amass the money needed for Hawkwood); the other was the otto della guerra ["eight men of war"], eight men appointed to manage the war against Gregory.
Gregory ultimately returned to Rome in January 1378. If he wanted to maintain his property in Italy, he was going to have to oversee it personally. In a sense, the Avignon papacy ended by default.
*Florence had an unexpected reaction to excommunication—unexpected to our modern ideas of how devout the Middle Ages were. Someday...