On 18 November 1302, Pope Boniface VIII issued the Papal bull Unam sanctam^[a] which some historians^[1] consider one of the most extreme statements of Papal spiritual supremacy ever made.^{[failed verification – see discussion]} The original document is lost but a version of the text can be found in the registers of Boniface VIII in the Vatican Archives.^[2] The Bull lays down dogmatic propositions on the unity of the Catholic Church, the necessity of belonging to it for eternal salvation, the position of the pope as supreme head of the Church, and the duty thence arising of submission to the pope in order to belong to the Church and thus to attain salvation. The pope further emphasizes the higher position of the spiritual in comparison with the secular order.

The bull was promulgated during an ongoing dispute between Boniface VIII and Philip the Fair, King of France.^[3]

As long as England and France were at war with each other, neither likely to participate in any expedition to the Holy Land. Benedict sent cardinal nuncios to each court to broker a truce.^[4] When this failed he then tried to get the parties to come to terms by cutting off some of the revenues financing the conflict. On 5 February 1296, Bonifice issued the papal bull Clericis laicos forbidding clerics, without authority from the Holy See, to pay to laymen any part of their income or of the revenue of the Church; and likewise all emperors, kings, dukes, counts, etc. to receive such payments, under pain of excommunication.^[5]

Edward I of England responded with outlawry, concept known from Roman law. This effectively withdrew the protection of the English Common Law from the clergy.^[6] As Edward was demanding an amount well above the tenth offered by the clergy, Archbishopric of Canterbury Robert Winchelsey left it to every individual clergyman to pay as he saw fit.^[7]

Philip of France countered by prohibiting the export of gold, silver, precious stones, or food from France to the Papal States. This had the effect of blocking a main source of papal revenue. Philip also banished from France papal agents raising funds for a new crusade in the Middle East.

Boniface made the tactical error of backing down from some positions. In September 1296, he sent an indignant protest to Philip headed Ineffabilis Amor, declaring that he would rather suffer death than surrender any of the rightful prerogatives of the Church; but he explained in conciliatory terms that his recent bull had not been intended to apply to any of the customary feudal taxes due the King from the lands of the Church.

Then came the Jubilee year of 1300, that filled Rome with the fervent masses of pilgrims and made up for the lack of French gold in the treasury. The following year, Philip's ministers overstepped their bounds. Bernard Saisset, the Bishop of Pamiers in Foix, the farthest southern march of Languedoc was recalcitrant and difficult. There was no love between the south, that had suffered so recently with the Albigensian Crusade, and the Frankish north. Pamiers was one of the last strongholds of the Cathars. Saisset made no secret of his disrespect for the King of France. Philip's ministry decided to make an example of the bishop. He was brought before Philip and his court, on 24 October 1301, where the chancellor, Pierre Flotte, charged him with high treason, and he was placed in the keeping of the archbishop of Narbonne, his metropolitan. Before they could attack him in the courts, the royal ministry needed the Pope to remove him from his See and strip him of his clerical protections, so that he could be tried for treason. Philip IV tried to obtain from the pope this "canonical degradation". Instead, Boniface ordered the king in December 1301 to free the bishop to go to Rome to justify himself. In the Bull, Ausculta Fili ("Give ear, my son") he accused Philip of sinfully subverting the Church in France, and not in terms that were conciliatory:

Let no one persuade you that you have no superior or that you are not subject to the head of the ecclesiastical hierarchy, for he is a fool who so thinks.

At the same time, Boniface sent out a more general bull Salvator mundi that strongly reiterated some of the same ground of Clericis laicos.

Then, at the end of the year, Boniface, with his customary tactlessness having criticized Philip for his personal behavior and the unscrupulousness of his ministry (that being an assessment with which many modern historians would agree^{[citation needed]}), summoned a council of French bishops for November 1302, intended to reform Church matters in France — at Rome. Philip forbade Saisset or any of them to attend and forestalled Boniface by organizing a counter-assembly of his own, held in Paris in April 1302. Nobles, burgesses, and clergy met to denounce the Pope and pass around a crude forgery titled Deum Time ("Fear God"), which made out that Boniface claimed to be feudal overlord of France. The French clergy politely protested against Boniface's "unheard-of assertions". Boniface denied the document and its claims, but he reminded them that previous popes had deposed three French kings.

This was the atmosphere in which Unam sanctam was promulgated weeks later. Reading of the "two swords" in the Bull, one of Philip's ministers is alleged to have remarked, "My master's sword is steel; the Pope's is made of words." As Matthew Edward Harris writes, "The overall impression gained is that the papacy was described in increasingly exalted terms as the thirteenth century progressed, although this development was neither disjunctive nor uniform, and was often in response to conflict, such as against Frederick II and Philip the Fair."^[8]

Most significantly, the bull proclaimed, "outside of her (the Church) there is neither salvation nor the remission of sins". It is an extreme form of the concept known as plenitudo potestatis (plenitude of power); it declares that those who resist the Roman Pontiff are resisting God's ordination.^[9]

The bull also declared that the Church must be united, the Pope was the sole and absolute head of the Church:

Therefore, of the one and only Church there is one body and one head, not two heads like a monster.^[10]

The Bull also stated:

We are informed by the texts of the gospels that in this Church and in its power are two swords; namely, the spiritual and the temporal.^[10]

The swords being referred to are a customary reference to the swords yielded by the Apostles upon Christ's arrest (Luke 22:38; Matthew 26:52).^[2] Early theologians believed that if there are two swords one must be subordinate to the other. It^{[clarification needed]} then became a spiritual hierarchal ladder, the spiritual judges the secular "on account of its greatness and sublimity,^[2] while the lower spiritual power is judged by the higher spiritual power, etc.^[9] Thus, it was concluded, the temporal authorities must submit to the spiritual authorities, not merely on matters concerning doctrine and morality: "For with truth as our witness, it belongs to spiritual power to establish the terrestrial power and to pass judgment if it has not been good."

The bull ends:

Furthermore, we declare, we proclaim, we define that it is absolutely necessary for salvation that every human creature be subject to the Roman Pontiff.^[10]

In the bull, Boniface reiterates what popes since the time of Gregory VII had been declaring.^[11] Much of what is said can be taken from the writings of Bernard of Clairvaux, Hugh of St. Victor, and Thomas Aquinas.^[2] The bull also contains writing from the letters of Innocent III, who mainly reasserted the spiritual power and the "plenitudo potestatis" of the papacy.^[11] A voice heavily noticed in the bull is Egidius Romanus (Giles of Rome), who some hold might have been the actual writer of the bull.^{[12][page needed]} Giles, in On Ecclesiastical Power, voices the supremacy of the Roman Pontiff over the material world. His line of argument states that since the body is governed by the soul and the soul is governed by the ruler of the spiritual, the Roman Pontiff therefore is governor of both soul and body.

According to the Catholic Encyclopedia in the registers, on the margin of the text of the record, the last sentence is noted as its real definition: "Declaratio quod subesse Romano Pontifici est omni humanae creaturae de necessitate salutis";^[2] thus this phrase, like some in canonic scripture, may have moved from an original position as a marginal gloss to an integral part of the text as it has been accepted. Some believe that this is the only dogmatic definition in the bull because the rest is based on differing "papal claims of the thirteenth century".^[9]

Boniface's reputation for always trying to increase the papal power made it difficult to accept such an extreme declaration. His assertion over the temporal was seen as hollow and misguided and it's said^{[by whom?]} the document was not seen as authoritative because the body of faith did not accept it.^{[9][page needed][11][page needed]}

In response to the bull, Philip had the Dominican Jean Quidort issue a refutation. Pope Boniface reacted by excommunicating the king. Philip then called an assembly in which twenty-nine accusations against the pope were made, including infidelity, heresy, simony, gross and unnatural immorality, idolatry, magic, loss of the Holy Land, and the death of Celestine V. Five archbishops and twenty-one bishops sided with the king.

Boniface VIII could only respond by denouncing the charges; but it was already too late for him. On 7 September 1303, the king's advisor Guillaume de Nogaret led a band of two thousand mercenaries on horse and foot. They joined locals in an attack on the palaces of the pope and his nephew at the papal residence at Anagni, later referred to as the Outrage of Anagni. The Pope's attendants and his beloved nephew Francesco all soon fled; only the Spaniard Pedro Rodríguez, Cardinal of Santa Sabina, remained at his side to the end.

The palace was plundered and Boniface was nearly killed (Nogaret prevented his troops from murdering the pope). Boniface was subjected to harassment and held prisoner for three days during which no one brought him food or drink. Eventually the townsfolk, led by Cardinal Luca Fieschi, expelled the marauders. Boniface pardoned those who were captured. He was escorted back to Rome on 13 September 1303.^[13]

Despite his stoicism, Boniface was shaken by the incident. He developed a violent fever and died on 11 October 1303. In A Distant Mirror: The Calamitous Fourteenth Century, Barbara Tuchman states that his close advisors would later maintain that he died of a "profound chagrin".

Boniface VIII's successor, Benedict XI, reigned only nine months. He removed himself and the Roman Curia from the violence of Rome as soon as the Easter celebrations of 1304 were completed. But, on 7 June, 1304, from Perugia, he excommunicated Guillaume de Nogaret, Reynald de Supino, his son Robert, Thomas de Morolo, Peter of Gennazano, his son Stephen, Adenulph and Nicolas, the sons of a certain Matteo, Geoffrey Bussy, Orlando and Pietro de Luparia of Anagni, Sciarra Colonna, John the son of Landolph, Gottifredus the son of John de Ceccano, Maximus de Trebes, and other leaders of the factions who had attacked Pope Boniface.^[14][15] He died on 7 July, 1304. The Conclave to pick his successor^[16] was in deadlock for eleven months before deciding, under the intimidation of King Charles II of Naples, on Archbishop Bertrand de Got of Bordeaux, who took the name Pope Clement V.^[17] To please Philip IV of France, Clement moved his residence to Avignon. From this point until around 1378, the Church, in an effort to keep tensions loose with France, fell under the immense pressure of the French monarchy. Some theologians^{[clarification needed][who?]} feel this stemmed from Boniface VIII's and Philip IV's battle against each other. Philip was said to have held a vendetta against the Holy See until his death.^[11]

It was not just the French monarchy and clergy who disapproved of Boniface and his assertions. There were many texts circulating around Europe that attacked the bull and Boniface's bold claims for the power of the Papacy over the temporal. One of the more notable writers who opposed Boniface and his beliefs was the Florentine poet Dante, who expressed his need for another strong Holy Roman Emperor. His treatise De Monarchia attempted to refute the pope's claim that the spiritual sword had power over the temporal sword.^{[18][page needed]} Dante pointed out that the Pope and Roman Emperor were both human, and no peer had power over another peer. Only a higher power could judge the two "equal swords", as each was given power by God to rule over their respected domains.

• Pope Boniface VIII, Unam Sanctam, 18 November 1302