Medieval Treaty Obligation

Allen Z. Hertz was senior advisor in the Privy Council Office serving Canada's Prime Minister and the federal cabinet. Formerly he worked in Canada’s Department of Foreign Affairs and taught history and law at universities in New York, Montreal, Toronto and Hong Kong. He studied history and languages at Montreal’s McGill University (B.A.) and then did graduate work in East European and Ottoman history at New York’s Columbia University, where he received his M.A. and Ph.D. He later earned international law degrees from Cambridge University (LL.B.) and the University of Toronto (LL.M.).

Foreword

Most of the work for this paper was done in 1989, when I was a Visiting Fellow of Cambridge University’s Research Centre for International Law, now the Lauterpacht Centre. Recalled with gratitude are the kindness and cooperation afforded by Professor Sir Elihu Lauterpacht and the Centre’s staff. A footnoted version of this article was published in Connecticut Journal of International Law, Vol. 6 (1991), pp. 425-443.

Modern international law places special emphasis on the treaty as a legal source and insists that treaty obligations are legally binding. The late Professor Clive Parry (1917-1982) used to teach Cambridge University law students that before 1919 the moral requirement to fulfill treaty obligations was "binding in honour alone." He also argued that before the First World War publicists and diplomatists regularly excluded treaties from the ambit of international law, which was then conceived to be primarily customary.

This paper on the Middle Ages is part of a larger project that tests the validity of Parry's significant argument, via an examination of treaty obligation in the medieval, classical and modern periods of international law. The Middle Ages are understood as ending with the 16th-century Protestant Reformation. The classical period of international law terminated abruptly with the 1919-1920 Paris Peace Conference, the several treaties of which each included the Covenant of the League of Nations.

Introduction

The present study argues that the medieval treaty was binding in canon law principally by virtue of ecclesiastical jurisdiction over solemn oaths. As Christians, kings were said to be subject to the pope "by reason of sin" (ratione peccati), in this connection, perjury and oath breaking. Also on this website are a dozen March 2012 postings entitled "Treaty Obligation from the Protestant Reformation to 1919" that describe how the Protestant Reformation destroyed Christendom’s legal unity, thereby setting the stage for the emergence of the classical system of international law. As in the Middle Ages, post-Reformation lawyers continued to intone “agreements must be kept” (pacta sunt servanda). But, by contrast with medieval law, the classical framework notably offered no legal remedy for breach of treaty.

The March 2012 postings entitled "Treaty Obligation from the Protestant Reformation to 1919" show that, for approximately 400 years, the moral requirement to fulfill treaty obligations was "binding in honour alone." Therefore, the classical context is one in which particular attention must be paid to the meaning of “honour” and its significance in international law and relations. This topic is thoroughly explored in “Honour’s Role in the International States’ System,” which was posted on this website in November 2009. Also relevant is the February 2012 posting entitled "Peace Bilateral and International: Birth of 'International Peace and Security' as Legal Order and Term of Art."

Those three postings identify the treaty as a major beneficiary of the international-law revolution that occurred at the end of the First World War. The aristocratic emphasis on honour was then replaced by a bourgeois focus on law. The treaty then became an integral part of international law and remarkably rocketed into the number-one position among the sources and evidences of international law. Also there emphasized is the understanding that one of the principal purposes of first the League of Nations and then the United Nations (UN) was to make treaties "legally" binding, as they had been during the Middle Ages.

What Was the Pope’s Jurisdiction?

What today we call “international law” began to emerge in the period from the mid-16th century to the early 17th century. But, casting his mind back to the Middle Ages, Gottfried Wilhelm Leibniz (1693) said that “the divine positive law contained in the sacred Scriptures” was a common tie linking Christians. To the Old and New Testaments, he added the canon law as “the pontifical legislation, to which kings and peoples submit themselves.” On this basis, Leibniz thought that:

before the schism of the last century, it seems to have been accepted for a long time (and not without reason) that a common republic of Christian nations must be thought of.

Leibniz’s Respublica Christiana is an historical commonplace. But, it took systematic study for 19th- and 20th-century scholars to recover two key concepts:

• Medieval society (i.e. Christendom) was understood theologically as Christ’s body (Corpus Christi) and legally as a body ("the church" as a corporation) coextensive with the entire community of the faithful.
• Within Christendom, the pope claimed superior judicial and legislative powers expressed through binding decretal letters prepared by a professional chancery, in its heyday unequalled in Europe.

According to Walter Ullmann (1975): "The basic assumption behind every decretal was papal primacy in the shape of universal monarchic government to be exercised over society which was the Church as the body of clergy and laity alike." A similar understanding had earlier caused Sir Paul Vinogradoff (1923) to include "the world State of medieval Christendom" as one of the "historical types of international law."

The relationship between the universal church’s canon law and a specific territory’s secular law received representative expression in the work of the renowned legist and canonist Baldus De Ubaldis (1327-1400). He believed that, if absolutely necessary, the pope had the power to depose even the Holy Roman Emperor. Secular rulers and secular law were said to be subject to higher norms embodied in natural law, ius gentium and divine law, including canon law. Baldus conceded that secular rulers could legislate contrary to higher norms, but he argued that such legislation would be invalid. In other words, canon law was seen as a limit to secular law and jurisdiction. Canon law and secular law were said to apply in their respective spheres. However, Baldus stressed that the ecclesiastical courts could always take jurisdiction by reason of sin (ratione peccati). Canon law was said to be supreme in spiritual matters, the extent of which was to be defined by the ecclesiastical courts. According to Baldus:

A spiritual case impinging upon a civil one is not heard by a civil, that is a secular judge; but, on the contrary, if a case for a civil court impinges upon a spiritual case, it belongs to the spiritual judge.

 Finally, he claimed that residual power belonged to the church insofar as ecclesiastical authorities could exercise full jurisdiction over any territory lacking secular jurisdiction.

Baldus De Ubaldis (1327-1400)

From the mid-12th century to the eve of the Reformation, the popes were generally lawyers, sometimes even jurists of great distinction. According to Harold Berman (1983):

The papal court of general jurisdiction, both original and appellate, was called in the 12th century, the consistory; the pope himself presided over it. As papal jurisdiction expanded, the popes began to appoint judicial auditors (cardinals, bishops or simple chaplains), whose decisions were binding, subject to papal ratification. In the 13th century, the auditors became a permanent court, called the Audience of the Holy Palace, which deliberated as a body (often divided into sections), and at the end of the century a separate court of appeals was established for civil and criminal cases. In the 14th century a supreme court was established, eventually named the Rota.

The papal court was an institution in many respects comparable to modern international tribunals. According to Walter Ullmann (1970):

The papal court could act both as a tribunal of first instance and as an appellate court. It could become active on its own motion or upon the complaints of a party, be that an individual or a group or a corporate body or a Ruler. Its jurisdiction was unrestricted as to subject matter, persons or territories. No prescriptive time impeded its working. 

The papal court had: (i) compulsory jurisdiction over all Christians including kings; (ii) a mixed judicial-legislative competence to make final legal pronouncements of universal applicability; and (iii) the power to enforce decisions via spiritual sanctions like excommunication and interdict.

What Were the Papal Sanctions?

An “interdict” was a negative command or prohibition directed against an individual, a group or a place. For example, Pope Innocent III placed all of England under an interdict from 1208 to 1213. In the affected area, the use of sacred things was forbidden. The faithful were thus unable to enjoy divine services, including celebration of the mass, public processions and the benediction of the blessed sacrament. Pope Innocent IV (1245) said interdict was an appropriate penalty for the wrongdoing of corporate bodies like cathedral chapters, peoples or tribes.

The most serious ecclesiastical sanction, “excommunication” separated the offender from the communion of the faithful. Apart from general ostracism, excommunication meant exclusion from: Christian burial; public acts of prayer and worship; and the sacraments, including the Eucharist, in which bread and wine were taken as Christ’s body and blood. Excommunication signified the loss of church membership rights. But, the delinquent remained subject to ecclesiastical jurisdiction and bound to Christian obligations. The medieval incorporation of the individual into the church as the body public explains excommunication’s gravity as a legal and social sanction. Sometimes called “the papal arms,” excommunication had a powerful effect precisely because it was based on the religious faith that was then fundamental to society at large.

Excommunication was politically decisive because an excommunicate ruler “was to be shunned by his ministers and his officials and he was to be refused obedience.” Canon lawyers generally agreed that Christians were absolved from their loyalty oaths to an excommunicate king. For example, Pope Innocent IV (1245) excommunicated the Holy Roman Emperor Frederick II. The papal sentence absolved subjects from their oaths of allegiance and instructed them neither to obey Frederick nor to recognize him as emperor or king.

There was agreement between Baldus and his teacher, the civilian Bartolo da Sassoferrato (1314-1357), that an excommunicate ruler could not legislate and an excommunicate judge could not pronounce a valid sentence. Diplomatic relations and treaty making with an excommunicate king were strictly forbidden. This ban was reflected in the coronation oath (1310) of the Holy Roman Emperor Henry VII. He had to promise that he would never enter into relations, alliance or agreement with anyone standing outside the community of the Catholic faith. And, a sentence of excommunication voided prior agreements. For example, “earlier alliances were broken off and treaties that had been painfully negotiated were trampled underfoot,” when Pope Clement V (1309) excommunicated leading Venetians and placed an interdict on the Republic of Venice. Sworn agreements with England’s King Henry VIII were specifically invalidated when he was excommunicated by Pope Paul III in 1535. Furthermore, the papacy might proclaim a crusade against a king who continued to defy one year of excommunication and interdict.

Medieval Treaties Binding in Canon Law?

The world was familiar with the treaty and the question of treaty obligation long before the emergence of the modern State and the pluralistic States’ system with its distinctive international law. In the early 19th century, international-law scholar Henry Wheaton wrote:

The law of nations acknowledged by the ancient Greeks and Romans was exclusively founded on religion. The laws of peace and war, the inviolability of heralds and ambassadors, the right of asylum, and the obligation of treaties, were all consecrated by religious principles and rites. […] Treaties were sanctioned with solemn oaths, the violation of which it was believed must be followed by the vengeance of the gods.

Wheaton here referred to classical antiquity, but the remarks are an excellent starting point for an understanding of the medieval treaty, which was an agreement between Christian kings, concluded within the context of their common faith. The legitimacy of a treaty between a Christian and a non-Christian ruler was therefore problematic. Medieval history records many agreements between Christian and Muslim potentates. However, a ban on relations between the faithful and unbelievers, prohibita communio fidelis cum infideli, was generally the church’s theoretical position.

The medieval treaty was a holy contract inseparably bound up with the key institution of the sacred oath and the canonical provisions punishing perjury and other oath violations. According to the New Catholic Encyclopedia:

An oath is the invocation of the name of God in witness to the truth. It may be taken only in accordance with the truth, with prudence, and with justice. The intention of calling God to witness to the truth of a statement (assertory oath) or a promise (promissory oath) must be sincere and sufficiently manifest to others in words or unmistakable signs. A person is bound by a special and personal obligation of religion to fulfill what he has freely promised by oath to do.

In the strictest sense, perjury is lying under oath, i.e. intentionally swearing to the veracity of a statement known to be false. According to the New Catholic Encyclopedia:

A lying, or perjured, oath is always a mortal sin because it involves contempt for God and disrespect for his attributes. The perjurer asks God to be witness to a lie or supposes that God can be deceived. Perjury is one of the most serious offences against the virtue of religion; it contains the malice of contempt for God.

There is clearly an important distinction between subsequent, willful failure to fulfill a sworn promise and the making of a knowingly false statement under oath. The latter constitutes the grave offence of perjury; the former is also a sin, but its seriousness depends on the circumstances of the particular case. But, the Middle Ages significantly tended to use “perjury” broadly to cover both sworn falsehood and subsequent willful failure to perform an oath obligation. Willful violation of a promissory oath is still regarded as perjury in some European countries.

The Bayeux tapestry indicates that Harold swore an oath to back his promise to help William Duke of Normandy become King of England

According to Ernest Nys (1894), the oath necessarily gave the medieval treaty a “religious character” which allowed the papacy to take judicial notice of any breach of treaty. For Joycelyne Dickinson (1955), the key point about medieval thought on treaties was that:

They were invested with a special solemnity, because they were usually ratified by oaths, to break which involved the sin of perjury which was a spiritual offence. This was true whether the oath had been taken at a great ceremony, in the hands of a papal legate or senior ecclesiastic, and before a great gathering of people, or whether it was exacted by a local official in pursuance of a clause in the treaty calling for widespread oath-taking in the dominions of the contracting parties. In either case, the oath to the treaty would be a sanction which could, in the last resort, be enforced with heavy ecclesiastical penalties, but which was, in the first place, a matter of conscience.

The medieval approach to treaty obligation was well expressed in an oration (1518) of the Tudor divine and diplomatist Richard Pace. He preached on the “Universal Peace” between England and France in the presence of England’s King Henry VIII, his Lord Chancellor Thomas Wolsey, the Papal Legate Cardinal Lorenzo Campeggio and the French ambassadors. The sermon was at London’s Saint Paul’s Church, where “this most religious treaty” between Kings Henry VIII and Francis I was proclaimed and ratified.

O happy pair of Kings! You are today about to give a most auspicious beginning to three things: to the treaty; to faith; and to peace: to the treaty, that it shall be entered into with holiness; to faith, that it shall be sincere and inviolable; to peace, that it shall be perpetual. […] So may immortal God bring it to pass that the joy we feel at this most healthful peace, formed and entered into in this church today, shall be solid and perpetual for all Christians. Of this inestimable blessing the sacred oaths with which this holy treaty has been confirmed give me a sincere hope. He who shall not fear to violate these oaths shall sink his body and soul together into the depths of Hell and the Gehenna of fire.

How Were Medieval Treaties Made?

Used as examples of medieval treaty making will be the Paris Treaty (1259), the Arras Treaty (1435) and the Cateau-Cambrésis Treaty (1559). These agreements are featured for three reasons. First, they have been examined in detail by modern historians. Second, their parties (England, France, Burgundy, Spain) were major participants in the European diplomacy of their day. Third, from a political viewpoint, they were substantively important as peace treaties.

Through the Paris Treaty (1259), England’s King Henry III and France’s King Louis IX sought to end a half-century dispute over Normandy, Anjou, Touraine, Maine and Poitou. The treaty was made in four main stages: pax inita (beginning peace); pax firmata (affirming peace); ratificacio (ratification); and publicacio (publication).

Pax inita: In 1257 papal pressure pushed King Henry III to Paris pourparlers. The English king (May 1258) gave five envoys letters of proxy (littere procuratorie) with full powers (plena postestas) to act on his behalf. Simon de Montfort, Hugh Bigod, Peter of Savoy, and Guy and Geoffrey de Lusignan were authorized to go to Paris to extend the truce and negotiate a definitive peace. Furthermore, the king empowered them to swear solemn oaths on his soul (juramentum in animam regis) that he would keep the truce and abide by the treaty terms. Observed by papal envoys, bilateral negotiations (tractatus) yielded articles of peace (composicio pacis) passed under the seals of the Archbishop of Tarentaise, probably acting for Henry III, and the Archbishop of Rouen for Louis IX. The document was then kept safe in the Paris Temple which was headquarters of the Knights Templar, a crusading order directly under the Pope’s authority.

Pax firmata: On May 28, 1258, the French and English delegations met with Louis IX. In Henry III’s name, Simon de Montfort, Peter of Savoy and Hugh Bigod swore that the English king would fulfill the agreed terms, provided that Louis IX would accept the treaty by Candlemas (February 2, 1259). The three English envoys gave Louis IX a sealed document containing the articles of peace and the text of their oaths. In Louis IX’s name, two French negotiators then swore that their king would fulfill the agreed terms on two conditions. First, for his remaining territory in France, Henry III had to do homage to Louis IX. Second, Henry III and his sons had to deliver letters patent recording their personal oaths to observe the treaty. The articles of peace and the oaths sworn by the French negotiators were then embodied in a sealed document given to the English envoys.

Around Candlemas 1259, three French envoys arrived in England where they announced that Louis IX had accepted the treaty. Henry III designated William de Fortibus and Humphrey de Bohun as “proctors” with full powers to swear on his soul that we would fulfill the treaty terms. On February 17th the two proctors took the oath at Westminster in the presence of Henry III and the French envoys. The text of the oath was then recorded in a document which was sealed and given to the French delegation. In subsequent separate ceremonies, Henry III’s two sons Edmund and Edward swore that they too would observe the treaty. Letters patent recording Edmund’s oath were carried to Louis IX and there must have been a similar document for Edward.

Ratificacio and publicacio: Louis IX received from the English baronial council a paper confirming the articles of peace and from Edward and Edmund sealed documents indicating acceptance of the treaty. Through envoys, the two kings exchanged ratification instruments in October 1259. Henry III travelled to Paris, where he met with Louis IX and participated in a ceremony publishing the treaty on December 4, 1259. Louis IX then received homage from Henry III for his remaining territory in France.


1259 King Henry III's homage to Louis IX

1435 Arras Treaty “Religious”?

The Arras Treaty was concluded between Charles VII, King of France, and Philip III, Duke of Burgundy. The Hundred Years’ War (1337-1453) found its turning point, because Burgundy decided to quit the 1420 Treaty of Troyes -- the alliance with England that had almost defeated France. The delegations met in the Saint Vaast Abbey, where mediation was provided by Cardinal Nicolo Albergati acting for the pope and the Cardinal of Cyprus for the General Council of the Church at Basle. The text was agreed after lengthy negotiations, in which the mediators played an active role. The two cardinals may even have met with each of the parties separately, after the fashion of the cross-examination of witnesses by judges in ecclesiastical courts. In article 40, the parties acknowledged that breaches would be sanctioned by interdict and gradually intensifying penalties of excommunication (aggravatio and reaggravatio). Vassals would be absolved from their loyalty oaths to the party beaching his promise. Furthermore, principal vassals would be required to ratify the treaty and swear to keep the peace. They would also be obliged to accept a positive duty to renounce their allegiance should their ruler prove to be a treaty breaker (articles 39, 41).

The document was promulgated before a great assembly in the Saint Vaast Abbey Church on Saint Matthew’s Day (September 21st). Duke Philip III and the French ambassadors were asked whether they would faithfully observe the oaths which they were about to take. The Cardinal of Cyprus celebrated the mass of the Holy Spirit. The gospel was read by the Abbot of Saint Vaast and the epistle by the Abbot of Saint Nicholas of Reims. The Duke’s confessor, the Bishop of Auxerre, preached a sermon on reconciliation and fraternal union. The Cardinal of Cyprus presented a cushion bearing a golden cross and the Eucharist. Duke Philip III swore a solemn oath that he would forget his father’s assassination (1419) and pardon the guilty. Acting for the King of France, the Dukes of Bourbon and Richemont together put their hands on the cross and asked Duke Philip III to forgive King Charles VII for the 1419 murder. The two cardinals placed a hand on Philip III’s head and absolved him from the oath that he had taken to the 1420 Troyes Treaty with England. The cardinals repeated the absolution rite for the Burgundian lords who had also taken personal oaths to the Troyes Treaty. There followed an hour-long reading, first of the two cardinals’ respective papal and conciliar procurations, and then of the text of the new Arras Treaty. The congregation cried “Noel!” which, in medieval French, was figurative usage expressing joy at the final arrival of a long-awaited happy event. Duke Philip III swore to uphold the new treaty by an oath made on the gospels held by the two cardinals. His oath was then recorded in ratification letters issued that same day. Acting for King Charles VII, the French ambassadors solemnly swore to fulfill the new treaty and these oaths were also documented. The entire congregation was asked to raise the right hand and, in common, to take an oath to respect the treaty. The ceremony was concluded with the benediction.

Philip III Duke of Burgundy

Duke Philip III was eager to have the Arras Treaty ratified by both the pope and the Council of Basle. The mission to the pope at Florence was successfully entrusted to the Priest of Autun, Nicolas Goguet (November 1435). At the same time, Besançon Dean Jean Fruyn secured letters of ratification from the Council of Basle.

King Charles VII

France’s King Charles VII ratified the Arras Treaty in Saint Martin’s Church, Tours (December 10, 1435). Archbishop of Crete, Fantinus Valareso said mass for a congregation, including the princes and nobles. Also present were the Burgundian ambassadors, Bishop Rolin of Noyon and Jean de Croy. The royal chancellor summarized the treaty and explained its purpose. Kneeling before the archbishop’s chair, King Charles VII swore to keep the treaty with an oath which he gave, while touching the New Testament lying on the archbishop’s lap. The same oath was taken individually by the princes and principal nobles, and the rest of the congregation raised the right hand and swore a general oath. They all then shouted “Noel!” King Charles VII shook hands with the Burgundian ambassadors and an organ accompanied singing of Te Deum.

1559 Cateau-Cambrésis Treaty Religious?

The agreement was a landmark in the long-standing struggle between two powerful European dynasties, the Valois (France) and the Habsburgs (Spain and the Low Countries). Negotiations began at the Cistercian Abbey of Cercamp and continued at the bishop’s residence at Le Cateau near Cambrai. On April 3, 1559, ambassadors of King Henry II of France and King Philip II of Spain signed the articles of peace, which had been engrossed on parchment. Although the Protestant Reformation had already torn the fabric of Europe’s legal unity, “the Most Christian King” of France and “the Catholic King” of Spain both remained firmly within the framework of the Roman Church.

The treaty was proclaimed on the same day in Le Cateau’s parish church, in a ceremony that included the Te Deum and mass. Religion was also reflected in the treaty’s preamble:

God has moved two great Princes… to seek an end to the disputes and differences of the war between them, and to transform it into a good, final, complete, sincere and durable Peace.

The medieval worldview lived on in the stipulation that the monarchs swear solemn oaths:

They [the signatory ambassadors] also undertake that the Catholic King shall, as soon as can be, take an oath to the treaty, in the presence of the representatives of the Most Christian King, on the Holy Gospels, and the Canon of the Mass, and on his honour. The Most Christian King shall do likewise, in the presence of the representatives of the Catholic King.

King Philip II ratified the treaty at a ceremony in the Coudenberg Palace Chapel at Brussels, on Whit Monday (May 15, 1559). After mass was said by the Bishop of Arras, Antoine Perrenot de Granvelle, King Philip II and the French ambassadors approached the high altar. Placing his hand on what was believed to be a relic of the true cross, the King of Spain promised to observe the treaty’s terms. On June 18, 1559, the King of France and the Dauphin performed the same rite in a ceremony at Notre Dame Cathedral in Paris.

Kings of Spain and France Embrace
Cateau-Cambrésis Treaty 1559

Kings Lacking Jurisdiction over Treaties?

The medieval concept of sovereignty was fundamentally personal, i.e. the sovereign was identified with the ruler as a natural human being. The medieval lawyer tended not to distinguish between public and private law, between a diplomatic envoy and an ordinary agent. For example, arbitration between two private individuals or between two rulers followed the same procedure, drawn from Roman law. Within this context, it is hardly surprising that treaties were considered to be nothing more than the contracts of kings. This perspective explains how the Roman ius gentium -- a body of private law governing individuals, their transactions and property -- was later able to father the system of public law for independent States. But, for understanding medieval treaty obligation, it is far more significant to appreciate that there was then an identity of contract and treaty. The former may therefore be used to explain the latter. In other words, the juridical position of the medieval treaty can be fixed by turning to medieval material on the law of contract.

For example, Baldus believed that a prince’s contracts were binding in both natural law and ius gentium. This emerges from his analysis of the feudal relationship. According to Joseph Canning (1987):

Baldus like all jurists sees the feudal bond as being based pre-eminently upon the most fundamental legal relationship, contract, without which human intercourse and society would be impossible. The sanctity of contract, and the fides involved in keeping it, are so fundamental that they are seen as the product of ius naturale or ius gentium, and are prior to any positive-law power possessed by the emperor, and limit him as anyone else. Thus, the divinely approved commission of power to the emperor does not include the plenitude of power over contracts, and especially feudal ones, a limitation he shares, for instance, with the king of France -- in feudal matters, both must observe due process of feudal law.

With reference to the jurisdiction of the secular ruler, Baldus was emphatic: “God has subjected the laws to him, but has not subjected to him contracts by which he is bound.” And, elsewhere he said: “Although the emperor is not bound by positive law, he is bound by the law of contract.” Furthermore, Baldus argued that contracts relating to the nature of the ruler’s office are also binding on his successors. This legal opinion was given for the feudal nexus between lord and vassal -- a relationship between superior and inferior. As a contract between equals, a treaty between two kings would be an a fortiori instance of his argument. Consequently, Baldus would have had no hesitation affirming that secular rulers are also bound by their treaties.

Papal Jurisdiction over Treaties?

Studying medieval diplomacy, Donald Queller (1967) concluded that, “truces, treaties and alliances are merely special forms of conventions or contracts.” This view is supported by a look at treaty-making procedures, which used instrumentalities drawn from private law. For example, “procuration” was a private-law institution that authorized an agent with full powers (plena postestas). From Roman law, procuration passed into diplomatic usage, probably via canon law:

The procurator was a sort of agent, used primarily in business affairs or before a court. The identical instrument was, however, gradually found serviceable for governmental administration or diplomacy.

In other words, procurators were first employed for negotiating private contracts for their principals and only later for treaties between rulers.

Canon law saw no difference between a treaty and a contract. “Agreements must be kept” (pacta sunt servanda) was the principle of penitential discipline that applied to either treaty or contract. The canonical theory was that “an oath and a promise are equal in the sight of God… not to fulfill the obligations of a pact is equivalent to lie.” Depending on the circumstances, the breach of a promise might itself be grave enough to deserve ecclesiastical censure by reason of sin (ratione peccati). But, in practice, the parties to treaties and contracts were not satisfied with simple promises or pacts. They were Christians who, frequently for contracts and always for treaties, reinforced their obligations with the swearing of solemn oaths. This was the decisive aspect which ensured that the church was allowed to decide both contract and treaty disputes. Oaths including pledges of faith were by reason of subject matter (ratione materiae) under ecclesiastical jurisdiction.

In the New Testament (Matthew xvi, 18-19), Saint Peter is promised the keys to the kingdom of heaven and told: “Whatsoever you will bind on earth will be bound in heaven and whatsoever you shall loose on earth shall be loosed in heaven.” According to Walter Ullmann (1978), Saint Peter’s keys became in the pope’s hands keys of law (claves juris).

St. Peter's keys in the Vatican Coat of Arms

The pope was regarded as “living law” (lex animata) and “ordinary judge of all” (iudex ordinarius omnium). He had the power of binding and loosing (postestas ligandi et solvendi) which was understood juristically. As both legislator and judge, the pope could bind with law or judicial sentence. He could also loose by amending or repealing law or reversing a judicial decision. And, most relevant to matters of contract and treaty, the pope could release either a private individual or a king from a sworn obligation. This was a dispensation comparable to the solutio obligationis of Roman law. An excellent example is the aforementioned release of Duke Philip III of Burgundy from his sworn obligation to uphold the 1420 Troyes Treaty, the alliance with England.

The possibility of a papal dispensation was well known, so parties sometimes explicitly agreed to refrain from applying to the pope for release from a treaty oath. For example, precisely this stipulation was inserted into the 1360 Brétigny Treaty between the kings of England and France.

1360 Brétigny Treaty

The papacy was especially active in relation to treaties which feature frequently in the registers kept by the papal chancery. There are many examples of kings submitting their agreements to the pope for approval, confirmation, ratification, or nullification. In the late 15th century, France’s King Louis XI told his ambassadors that ratification by the pope was still the best way to ensure the performance of a treaty obligation.

Medieval Case Law for Breach of Treaty?

According to Harold Berman, cases alleging breach of a solemn oath (causa fidei laesionis seu perjurii), like other ecclesiastical causes, were started:

by filing a complaint in the court of the appropriate archdeacon or bishop, and an appeal could be taken by the losing party to the court of the appropriate archbishop and thence to the court of the pope in Rome…. The pope also exercised a universal original jurisdiction: the plaintiff could impetrate (procure) a writ from the papal curia nominating papal delegates to try any case locally. This, indeed, was quite common in cases involving considerable sums of money, as well as in cases in which the parties resided in different archbishoprics.

King John of England turned to the papal court at Rome to make a “denunciation” against King Philip Augustus of France. The allegation was that, in April 1202, Philip had resumed hostilities against John’s mainland possessions in contravention of a solemn truce, backed by the sacred oath of both parties. King Philip Augustus began by contesting the court’s jurisdiction. He argued that Rome had no right to interfere in a quarrel between kings and emphasized that John was also his vassal. Pope Innocent III replied with the decretal Novit ille (1204). The pope conceded that the Church had no business meddling in feudal affairs per se, but claimed jurisdiction, because the case involved a question of sin, i.e. the allegation of the breach of a solemn oath. Moreover, Pope Innocent III took this occasion specifically to affirm that the breaking of peace treaties (rupta pacis foedera) was subject to canon law on the facts of the case (ratione causae). A papal legate was therefore dispatched to Meaux, where a council began proceedings for "censures" against Philip Augustus. The French bishops then appealed to Rome, where representatives of both kings were summoned. Because John’s representatives failed to appear, King Philip Augustus won by default. This litigation was a reflection of the contemporary political constellation which cost King John most of his territories on the continent.

In 1337, France’s King Philip VI took away the Duchy of Guyenne from England’s King Edward III. The English considered this to be a violation of the treaties between England and France. A contemporary legal opinion advised Edward to appeal to the pope’s compulsory jurisdiction (full apostolic powers) by reason of sin (ratione peccati). The proposal envisaged a papal judgment ordering the King of France to restore the confiscated province on pain of excommunication and interdict.

Kings Wary of Pope’s Compulsory Jurisdiction?

Medieval legal sophistication is evident in the distinction which contemporaries made between the pope’s compulsory jurisdiction (full apostolic powers) and instances where the disputing parties agreed to submit their case to the pope for either mediation or arbitration. Medieval rulers sometimes volunteered to accept papal mediation or arbitration, but they were generally wary of compulsory jurisdiction flowing from the pope’s full apostolic powers. For example, Pope Boniface VIII (1295) sought to use his compulsory jurisdiction to order a peace treaty between England’s King Edward I and France’s King Philip IV. Despite application of ecclesiastical sanctions, Philip IV refused to obey the pope. However, Philip IV was willing to authorize Pope Boniface VIII to arbitrate in his private capacity as Signore Benedictus Gaytanus. “As if a private person” (tamquam in privatam personam), Pope Boniface VIII gave his arbitral award on June 27, 1297.

The distinction between the pope’s compulsory jurisdiction and voluntary submission to papal mediation or arbitration was again recognized in 1300, when King Edward I invited Pope Boniface VIII to settle a new dispute with the King of France. The pope replied to the English envoys that he had considered the matter carefully, but did not believe that it could be settled through mediation because the French would make unreasonable demands:

And, if we will arbitrate, the French will not execute our award; it would not even be possible to force them to do it by making them pay a fine, about which they will worry very little. This is why we believe that it would be good if we would use our full apostolic powers. For us to be able to do this, it would be necessary that complaints against the king of France are formulated for us and that it is alleged that he has committed a sin by wrongfully retaining territory belonging to the king of England. [...] If the king of France argues that we do not have the authority to intervene in questions of fiefs, we will reply that we do by reason of sin.

Treaty Obligation's Link to the Search for Peace

Modern international law says the system’s rules are based on the consent of States expressed in their practice. And, the Statute of the International Court of Justice regards the best evidence of State practice to be treaties as “establishing rules expressly recognized by the contesting States.” The preamble to the UN Charter points to “respect for the obligations arising from treaties” as one of the organization’s main aims. UN Charter, Article 102 requires that every treaty made by UN Members be registered with the Secretariat and published. Article 36 of the Statute of the International Court of Justice invites States to opt to recognize the court’s compulsory jurisdiction over treaty interpretation.

The UN Charter is itself a treaty. Although it deals with a variety of additional topics like human rights and economic and social development, the UN Charter focuses on maintenance of international peace and security. Thus, UN Charter, Article 2(4) prohibits the “use of force against the territorial integrity or political independence of any State.” Because UN membership is near universal, an act of aggression is normally also a treaty violation. The point is fundamental, because peace treaties have always been among the most significant agreements between States. This invites the key question: are peace treaties legally binding? Is there now an effective international remedy for an egregious violation of the treaty obligations that States accepted when they joined the UN?

As students of international law and politics soon learn, the answer is complicated, and can only reveal a varying gap between theory and practice, aspiration and performance. In the Middle Ages, there was also appreciation for the uncomfortable gap between theory and practice. But, the medieval search for peace continued even though the goal seemed impossible to attain. Our own century shares with that earlier age the attempt to make treaties binding in law. In measuring our own task and judging our accomplishment, can we ignore the efforts and experience of those who did the same work not so long ago?