Question: Why did the medieval Popes leave Rome to live at Avignon? Under what circumstances did they return?
Answer: Fourteenth century Rome was a dangerous place. Pope Boniface VIII died in 1303, shortly after escaping from the agents of the French king. There were factions at war with the Emperor, who claimed to be King of Rome. There were factions at war with the Pope over his claims to rule the Papal States. Other factions demanded the return of the Pope and clergy to Christlike poverty and spirituality. France, the Empire, and the Papacy simultaneously claimed many of the same territories throughout Italy. Cities were at war with other cities, and families were at war with other families. The bubonic plague hit Europe in 1348, striking crowded cities like Rome much harder than the countryside. The "age of the martyrs" was closed, and the aristocratic Popes of the fourteenth century had no intention of re-opening it.
When elected, the archbishop of Bordeaux who became Pope Clement V (1305-1314)2 was in France. Relatively important dealings with King PhilipIV of France kept forcing him to postpone his move to Rome.3 As they occurred, Pope Clement filled vacancies in the College of Cardinals with Frenchmen. His successor, Pope John XXII (1316-1334) began the elaborate palace at Avignon, a city on the Rhône. Although located in modern day France, fourteenth century Avignon was in territory controlled by the Papal States. It was selected to give the Popes some measure of freedom from the influence of the French King, without the danger of returning to Rome.
John XXII organized a complex papal bureaucracy and took the appointment of bishops out of local hands, trying to make it the exclusive prerogative of the Papacy. This was intended to make the Papacy economically self-sufficient and to enable the Pope to deal with temporal rulers as the head of a centralized Church. His intentions may have been good, but what appeared to be Papal greed and self indulgence contributed to the political unrest and strengthened the secular rulers. It didn't help at all when he condemned as heretical the idea that our Lord and His Apostles did not own property.4
Innocent VI (1352-1362) sent delegates to Rome to rule in his name. Although the subject of a siege laid against the papal palace, he did not himself leave Avignon for Rome. Urban V (1362-1370) brought his curia to Rome but abandoned the City after three years unsuccessfully trying to establish his authority as a temporal ruler. Gregory XI (1370-1378) did the same, but died in Rome before he was able to return to Avignon.
The Election of Pope Gregory's successor signaled new difficulties. Urban VI (1378-1389) was elected by a conclave under the pressure of the Roman mob to appoint an Italian Pope. At first the Cardinals maintained that they had elected the former Archbishop of Bari of their own free will. But when the new Pope turned out to be tyrannical, inflexible, and sometimes violent, they began to reconsider the validity of his election. All but three of the Cardinals conducted a second election in the city of Anagni, declaring Urban deposed, and electing Clement VII (1378-1394). Clement soon returned to Avignon.
Both Urban VI at Rome and Clement VII at Avignon had reasonable claims to be Pope. They excommunicated each other and appointed their supporters as Cardinals. France, Scotland, and Spain supported the claims of Pope Clement, while England, the Empire, and most of Italy supported Pope Urban. This balance of power precluded any military solution to the problem of two Popes.
This "Western Schism" continued, even though there were no doctrinal differences between the two parties, even after the deaths of Urban and Clement. It was hoped, by the clergy on both sides, that the two men claiming to be Pope might resolve the issue by mutually agreeing to resign and allowing the two groups of Cardinals to jointly elect a single Pope. But both sides continued to elect Popes who refused to enter into such a compromise.
Finally, an attempt was made by the Cardinals of both sides to call an ecumenical Council to depose both Popes and elect a new one. The Council of Pisa elected AlexanderV in 1409, but that only made matters worse, for then there were three Popes! The situation was not resolved until the Council of Constance deposed all three and elected Pope Martin V (1417-1431). They risked having a fourth claimant, but with assistance from the Emperor the Church was able to gain recognition of Martin as the one single Pope. Gregory XII, the Roman Pope, approved the acts of the Council and resigned. Pope John XXIII, the successor of the Pope elected at Pisa, tried to flee but then did as Gregory did. In 1429 the last Avignonese Pope voluntarily resigned any claim he might have had.
Thus, the Papacy at Avignon, called the "Babylonian Captivity of the Papacy" by the scholar Petrarch, lasted somewhere between seventy and one hundred twenty five years. "Conciliarism," the deposition of popes by councils, however, would last quite a few more years. In 1439 the Council of Basel, deposed Pope Eugenius IV and elected the antipope, Felix V.6 Pope Pius II, earlier an advocate of "conciliarism," later condemned it when his own removal began to be discussed; the threat of Moslem invasion may well have helped him to consolidate his power.7 As recently as 1969, it was discussed in connection with liberal dissatisfaction over Pope Paul VI's continuing the Church's prohibition of artificial birth control.8
The Western Schism remains a curious part of history, eluding any clear conclusions about who was right and who was wrong. Only in the mind of God Himself can the election of Urban VI or Clement VII be determined. The Avignonese Pope Benedict XIII had Saint Vincent Ferrer for his confessor, while Saint Catherine of Siena advised Urban VI; both (unsuccessfully) urged their respective Pontiffs to adopt a more conciliatory attitude toward the other. Saint Colette, reformer of the Poor Clares, was under obedience to Benedict XIII. While generally recognizing the Roman line of Urban VI as the legitimate popes, the Catholic Encyclopedia refers to the Avignonese "residence of nine popes, Clement V .... Benedict XIII."9 Butler's says, "Because of their anomalous position this Clement VII and Benedict XIII are not referred to as antipopes but 'called popes in their obedience.'"10
Even the term "Western Schism" may not be fully appropriate. There was no doctrinal division, and no repudiation of the Papacy as an institution:
This dissension was called schism, but incorrectly. No one withdrew from the true Roman pontiff considered as such, but each one obeyed the one he regarded as the true pope. They submitted to him, not absolutely, but on condition that he was the true pope. Although there were several obediences, nevertheless there was no schism properly so-called.11
Perhaps the most important lesson to be learned from all of this is that "the gates of hell" will truly "not prevail" -- sometimes in spite of the gatekeepers.