Classic Works

Alberico Gentili, De Jure Belli Libri Tres (1588-1599)

Alberico Gentili (1552-1608) was an Italian jurist, practicing lawyer and professor of law at Oxford University, who is consistently mentioned as a key figure at the very origins of modern international law. Just a few years before Hugo Grotius, Gentili took substantial steps in the development of a secular jurisprudence.[1] Yet, his standing as a “pioneer” of the modern concepts of international law has been overshadowed by the preeminence of Grotius, the Dutch jurist generally regarded as the father of international law. According to Theodor Meron, Gentili was indeed “an original, enlightened . . . and eloquent writer who has not been given as much credit as his works clearly deserve.”[2]

The reason for Gentili’s disregard is due to the fact that until the end of the 19th century it was held that the modern law of nations only emerged in the 17th century. The Peace Treaties of Westphalia (1648) were commonly ascribed as having laid down the foundations of the modern states system and its law.[3] And whereas the writings of Grotius were discussed by a multitude of scholars and translated into many different languages, the works of Gentili were virtually forgotten for three centuries. It was not until 1874, when British Professor Thomas Holland delivered his inaugural lecture at Oxford University on Gentili, that interest in his work began to revive. Indeed, Gentili’s place in the history of international law owes much to Holland’s inaugural lecture and his scholarly edition of Gentili’s De Jure Belli Libri Tres in 1877.

Alberico Gentili was born in 1552, at San Ginesio, Italy. He studied law at the University of Perugia and became a judge at Ascoli. However, having embraced Protestantism, he was harassed bythe Inquisition, and obliged to leave his native country. He was welcomed in England in 1580, in the middle of Queen Elizabeth’s reign, when all Europe was in turmoil. In 1581, he received the degree of Doctor of Civil Law at Oxford University. In 1587, he was appointed Regius Professor of Civil Law at Oxford and later he became a member of Gray’s Inn, a Law firm in London, dedicated mainly to maritime cases.[4] In 1605, he became counsel for the King of Spain and represented the Spanish Embassy in London.

Gentili was, above all, a voluminous writer, and his works include a selection of legal, political and moral themes. However, the books of most direct significance for international law are three: De Legationibus (1585), concerned with the conduct of ambassadors, De Jure Belli Libri Tres (1588-89) written during English debates on issues of war prompted by the Spanish Armada, and Hispanicae Advocationis, a collection of legal opinions from his practice at Gray’s Inn, published in 1613 posthumously by his brother.

Before examining Gentili’s De Jure Belli work, it is important to briefly comment on the two other books mentioned above. A famous case gave life to his first book De Legationibus (On Embassies). In this book, Gentili presentssuccessfully the argument that the Spanish Ambassador should be expelled rather than punished for plotting against Queen Elizabeth. The circumstances in which he came to take up the work are indeed important. Yet most significant is the fact that this was his first important excursion into the field of international law.

In 1580, a Jesuit mission was sent to England to organize a Catholic movement against Queen Elizabeth. However, spies of the Queen had realized the coming danger, and just before the conspiracy for the assassination of Elizabeth could be carried out, compromising documents were discovered at the house of Francis Throckmorton, one of the active participants in the plot. Thus, all the plans of the conspirators were laid bare, including the role of Bernardino de Mendoza, the Spanish Ambassador at the court of Queen Elizabeth. An inquiry to Gentili was made to establish whether Mendoza could be sentenced to death in England. The pressure on Gentili must have been great to justify the punishment of the man who had violated the principles of hospitality in supporting the plot. However, he replied that no other action could be taken against Mendoza than dismissal from England. Out of his reply he developed his book On Embassies which contributed to the development of the concept of diplomatic immunity, “producing the first coherent study on diplomatic law.”[5]

While later working at Gray’s Inn, Gentili represented, with the approval of King James, the interests of Spain in cases heard by the English Court of Admiralty. He acted in this capacity from 1605 up to his death in 1608. His appointment to this post testifies to the high regard in which he was held as a jurist and to the reputation which his writings on international law had brought him at the time. The arguments which he made in support of Spanish claims, and the opinions which he wrote on other matters of international law and the law of the sea, were published posthumously at his request in the Advocatio Hispanica. This book is unique because, up until then, jurists developed works on general subjects or commentaries on particular laws or fictional legal cases. In his book Gentili presented the actual application of the principles of international law to concrete cases.

Gentili’s De iuri Belli libri tres (On the Law of War)[6] is composed of three volumes. The first volume focuses on the law relating to the right to go to war, or the ius ad bellum. The second volume examines the law governing the conduct of war, or the ius in bello. And the third volume explores the ius post bellum, the laws governing the conclusion of war and restoration of peace.

As Peter Haggenmacher argues, Gentili’s contribution to the law of war is the most renowned aspect of his work and remains important today.[7] He is the first writer to generalize some of the arguments which the Spanish theologian Francisco de Vitoria in particular had identified. As Anthony Padgen notes, Vitoria’s arguments had been intended to be applicable to all nations everywhere. However, the specific conditions with which Vitoria was primarily concerned were narrowly defined by the circumstances of the Spanish discovery of the Americas.[8]

Gentili constantly borrowed concepts from Roman law and applied the old learning to new questions posed by modern international affairs.[9] His method contributed to shaping his arguments in a refined and analytical way.[10] Yet, Gentili’s work is described as lacking a solid framework and his books can be characterized as “a collection of main questions, unified within a topical distribution and not dependent on a single principle.”[11] Gentili was a great law practitioner but he did not adopt an abstract theoretical perspective.[12] Moreover, his writing style may be considered obscure and characterized by ambiguity.[13] According to Andreas Wagner, in “…his elaborate style, Gentili used irony and sarcasm, rhetorical questions, and all sorts of other devices amply.”[14] Professor John C. Rolfe of the University of Pennsylvania was the translator of Gentili’s De iuri Belli and his translation reproduced, in idiomatic English, the idiomatic characteristics of the original in Latin. Rolfe added a few notes and an index of the authorities cited, together with a full general index of the subject matters. However, in a number of instances Gentili appeared to have relied upon his memory, and in several cases he stated that the books were not accessible to him.

What is important to recognize when examining De iuri Belli is that, whereas earlier scholars had addressed various international issues depending almost exclusively on the positions of the Roman Catholic Church, Gentili looked at international relations from a different perspective, namely, general principles independent of the authority of the Church. Thus, Gentili’s work reflects the secularization process of legal and political theory that was taking place in early modern Europe.[15]

Gentili rejected the idea that religion might have offered a just cause for war. He pointed out that war was not a religious phenomenon but a social one, and he noted that “since the laws of religion do not properly exist between man and man, therefore no man’s rights are violated by a difference in religion.”[16] Indeed, he was an advocate of complete religious liberty. One of Gentili’s most famous sentences was that of “[s]ilete theologi in munere alieno[17] translated as “[t]heologians, mind your own business.” The motto was directed against the group of Spanish theologians, among them Vitoria, who had written on the law of war and the legal basis of the Spanish conquest of the Americas. The standing of the school paralleled the growing prominence of Spain in the world, whose hegemony was fiercely opposed by the court of Queen Elizabeth in the England, where Gentili had found a home.[18]

The Italian jurist used civil law principles to develop a system alternative to the scholastic doctrine.[19] According to Pärtel Piirimäe, Gentili translated the humanist political philosophy, namely Machiavellism, Tacitism and reason of state, into legal terms.[20] Gentili stated that “as far as I am concerned, the subjects of others do not seem to me to be outside of that kinship of nature and the society formed by the whole world.”[21] His point of departure was the concept of gentes understood as “peoples” or “nations.” For Gentili gentes were bound as jus gentium. Gentili conceived the jus gentium in the sense of law between nations (jus inter gentes) governing the international community (societas gentium).

According to Gentili, the international community, also called the “global commonwealth,”[22] included all of the states of the world. Moreover, he considered that only states, as opposed to private individuals, were the subjects of this branch of law, and as David Kennedy notes this new focus on states “marked the beginning of the end of primitive legal scholarship.”[23] In De Jure Belli, Gentili stated that “all this universe, which you see, in which things divine and human are included, is one, and we are members of a great body…Now you have heard, that the whole world is one body, that all men are members of that body, that the world is their home . . . .”[24]

However, he did not develop a concept of the state as a legal subject (neither did he develop a concept of the “international” as in inter-state relations). According to Andreas Wagner, for Gentili sovereign states in their plurality were the pinnacle of the legal order and “his model of a globally valid ius gentium then fluctuated between being equivalent to private law, depending on individual acceptance by states and being natural law, appearing in a certain sense as a form rather of morality than of law.”[25] In his conception then “nations were always entitled to wage war.”[26] He suggested that “…war seems to be natural if you study nature… it is natural that men should disagree; and the result is war.”[27]

In the first volume of De Jure Belli, Gentili accepted that war could be just on both sides.[28] Vitoria had already conceded that, while a war could not be just on both sides objectively, for reasons of invincible ignorance and good faith, both parties might effectively be justified in fighting,[29] but only Gentili treated both parties as legally just enemies. For Gentili the necessity that made war just was one that called for the defense of the realm pre-emptively if that seemed necessary.[30] Consequently, he extended the concept of legitimate self-defense to cover even pre-emptive aggression.

Gentili’s doctrine of defensive war, and the right to go to war pre-emptively, constituted a breaking point, as previous theories about just war had been developed mainly by theologians. According to the theory of just war developed up until then only an injury could give rise to a just war.[31] Yet, for Gentili, pre-emptive action was permitted as it concerned the safety of the state: “No one ought to wait to be struck, unless he is a fool” and “a defense is just which anticipates dangers that are already meditated and prepared, and also those which are not meditated, but are probable and possible.”[32] In addition and closely related to the concept of pre-emptive action, Gentili also elaborated the concept of metus iustus or just fear, that is to say “the fear of a greater evil, a fear which might properly be felt even by a man of great courage.”[33]

In De iuri Belli, punishment was moved out of focus and self-defense became the dominant motive in formulating causes of war. Indeed, as Partel Piirimäe points out, Gentili  “. . . decoupled the notion of just war from the concept of punishment and described all just wars as defensive in character.”[34] Moreover, he was convinced that one had to assist one’s allies against an unjust attack, even if this has not been expressly stipulated because “good neighborhood imposes a duty of intervention.”[35]

In the second volume, Gentili’s main arguments were directed towards the importance of proportionate action in the conduct of war. He noted that when war had begun, it should be conducted in a sportsmanlike manner and he advocated the “plain, simple and magnanimous conduct of war.” He condemned the use of poisoned weapons, poisoning wells, the devastation of the enemy’s country and the destruction of public buildings. He argued that performing such acts would constitute the act of one who was mad and delirious. He explained that “to lay waste the crops, burn farmhouses and commit other outrages of that kind is a mark of extreme hatred” and only permissible as retaliation in extreme cases. He believed that “reprisals should be strictly proportionate to the damage inflicted by the enemy,” and that acts of violence should be avoided with regard to women and children.[36] He also wrote that prisoners of war should be treated humanely.[37]

In the third volume, Gentili focused on the body of law regulating the restoration of peace.[38] He devoted this volume to the law of victory and the law of peace, with chapter titles such as “Of the Vengeance of the Victor,” “On Exacting Tribute and Lands from the Vanquished,” “On Ensuring Peace for the Future,” and “Whether it is Right to Make a Treaty with Men of a Different Religion.” For the ius post bellum, which Gentili was the first to discuss extensively,[39] this meant that the terms of peace no longer relied on some objectively just state that had to be restored, but rather on the authority of the victor, whose title was constituted by his very victory, or on an agreement between the belligerents.[40]

It is important to note that Gentili conceived the three different stages of ius ad bellum, ius in bello and ius post bellum, not as separate, but as closely intertwined components of the law of war. Gentili argued that both in the ius ad bellum and the ius in bello, the parties should refrain from conduct that could prevent the restoration of peace.[41]

Unfortunately for Gentili, his De iuri Belli was veiled by the publication of Hugo Grotius’ On The Laws of War and Peace in 1625. Many scholars contend that Grotius reflected on and to an extent reshaped Gentili’s work. Petter Haggennmacher argues that “whatever other sources Grotius may have used, some of them no less important, little doubt is left as to Gentili’s central place.”[42] His conclusion is drawn from comparing Gentili’s De Jure Belli and Grotius’ work, a process which reveals the latter’s indebtedness to Gentili for methodology, structure, and argumentative patterns.[43] Scholars have noticed that even a superficial comparison of the two works shows that the third book of De Jure Belli ac Pacis Libri Tres by Grotius runs practically parallel with the second and third books of De Jure Belli by Gentili.[44]   Moreover, as Benedict Kingsbury notes, “the key features of the idea of an international society which is central to Grotius are all present in Gentili’s work, and Grotius adds little to Gentili’s account.”[45] Yet, in the prolegomena to his book, Grotius stated that “knowing that others can derive profit from Gentili’s painstaking, as I acknowledge that I have, I leave it to his readers to pass judgement on the shortcomings of his work as regards to the method of exposition, arrangement of the matter, delimitation of inquiries, and distinctions between the various kinds of law.”[46] Still, the indebtedness of Hugo Grotius to Gentili is a matter of much debate. One could argue that Gentili planted the seed and Grotius watered the plant, patiently tended to it and saw it flourished.

There is also an element of controversy in Gentili’s ideas due to some contradictions within his writings. While some scholars argue that he supported imperialist expansion,[47]other scholars and academics have an opposing view, highlighting that Gentili criticized hegemonic attempts and stating that he advocated pre-emptive action against Spain due to its expansionist policies, therefore favoring a balance of power.[48]

Beyond the debate and controversy, it is important to highlight two significant contributions of Gentili’s De iuri Belli. Firstly, the most important innovation in Gentili’s approach to the law of war was its opposition to the theological approaches that had discussed war and international relations in terms of a just, unitary global order.[49] Indeed, his work contributed to the emancipation of early international law from its theological foundations and paved the way for subsequent developments. Secondly, Gentili’s work contributed significantly to the amalgamation of the law of war. Indeed, he enunciated the law of war in the three separate and yet connected parts of ius ad bellum, ius in bello, and ius post bellum. He justified pre-emptive wars but emphasized the importance of moderation in the conduct of war. And finally, he emphasized a balanced position between a justification of punishment after war and a realization of the pragmatic need of avoiding the incitement of further violence.


[1] See Ingo Hueck, “The Discipline of History of International Law – New Trends and Methods on the History of International Law,” 3 Journal of the History of International Law (2001): 214–17.

[2] Theodor Meron, “Common Rights of Mankind in Gentili, Grotius and Suarez,” 85 American Journal of International Law (1991): 116.

[3]  Randall Lesaffer, “The Grotian Tradition Revisited: Change and Continuity in the History of International Law,” 73 British Yearbook of International Law (2002): 104.

[4] See Thomas E. Holland, An Inaugural Lecture on Albericus Gentilis (1874); H. Bull, B. Kingsbury, and A. Roberts (eds.), Hugo Grotius and International Relations (Oxford University Press, 2003). Also see Gesina van der Molen, Alberico Gentili and the Development of International Law (Leyden Sijthoff, 1968).

[5]  Artemis Gause, Gentili, Alberico, Oxford Dictionary of National Biography (2004).

[6] See, Alberico Gentili,  De Iure Belli Libri Tres, translated by John C. Rolfe, with an introduction by Coleman Phillipson (Oxford: Clarendon Press, 1933)

[7] Peter Haggenmacher, “Il diritto della guerra e della pace di Gentili. Considerazioni sparse di un ‘Groziano’,” in Il Diritoo Della Guerra e Della Pace di Alberico Gentili , Atti del Convegno Quarta Giornatta Gentiliana 9 (1995): 19.

[8] Anthony Padgen, The Burdens of Empires: 1539 to the Present (Cambridge: Cambridge University Press, 2015), Preface.

[9] Martti Koskenniemi, “International Law and Raison d’état: Rethinking the Prehistory of International Law,” in The Roman Foundations of the Law of Nations: Alberico Gentili and the Justice of Empire (Benedict Kingsbury & Benjamin Straumann eds., Oxford: Oxford University Press, 2010): 297.

[10] See Andreas Wagner, “Lessons of Imperialism and of the Law of Nations: Alberico Gentili’s Early Modern Appeal to Roman Law,” 23 European Journal of International Law (2012): 873, 875.

[11] Merio Scattola, Alberico Gentili (15521608), inThe Oxford Handbook of the History of International Law (Bardo Fassbender & Anne Peters eds., Oxford: Oxford Univ. Press 2012) at 1094.

[12] Id.

[13] Wagner, supra note 10.

[14] Id.

[15] Noel Malcolm, “Alberico Gentili and the Ottomans,” inThe Roman Foundations of the Law of Nationssupra note 9, at 127.

[16] Gentili, supra note 6, Vol. I at 41.

[17] Id. at 55.

[18] Martti Koskennemi, “The International Law and the Raison d’Etat,” in The Roman Foundations of the Law of Nations, supra note 9, at 299.

[19] However, it is important to note that the juridical doctrine initiated by Francisco de Vittoria and followed by others in the School of Salamanca represented the end of medieval concepts of law. Indeed, the position Vitoria carefully articulated shows the distinction between secular and spiritual power, a feature that distinguishes modern from medieval thought. In doing so, Vitoria freed his way for the construction of a new, secular law of nations. See Pärtel Piirimäe, “Alberico Gentili’s Doctrine of Defensive War and its Impact on Seventeenth-Century Normative Views,” in The Roman Foundations of the Law of Nationssupra note 9, at 187.

[20]For an explanation of these terms, see Id. at 194.

[21] Gentili, supra note 6, Vol. I, Chap.XVI.

[22] Andreas Wagner, “Francisco de Vitoria and Alberico Gentili on the Legal Character of the Global Commonwealth,” 31 Oxford Journal of Legal Studies (2011): 581.

[23] David Kennedy, “Primitive Legal Scholarship,” 27 Harvard International Law Journal 1, (1986): 58–59.

[24] Gentili, supra note 6, at 67.

[25] Wagner, supra note at 22.

[26] Gentili, supra note 6, at 112-124.

[27] Gentili supra note 6, Vol. II at 53.

[28] Id. Vol. I at 32-33.

[29] Francisco de Vitoria, Political Writings (A. Pagden and J. Lawrance eds, Cambridge: Cambridge University Press, 1991).

[30] Gentili supra note 6, Vol. I at 83-85.

[31] Partel Piirimae, “Alberico Gentili’s Doctrine of Defensive War and its Impact on Seventeenth-Century Normative Views,” in The Roman Foundations of the Law of Nationssupra note 9, at 187.

[32] Id. at 198 citing Gentili’s De Jure Belli.

[33] Id.

[34] Id. at 199.

[35] Gesina van der Molen, Alberico Gentili and the Development of International Law (Leyden Sijthoff, 1968), 136.

[36] Gause, supra 5note, at 4.

[37] Id.

[38] Gentili, supra note 6.

[39] Randall Lesaffer, “Alberico Gentili’s ius post bellum and Early Modern Peace Treaties,” in The Roman Foundations of the Laws of Nations, supra note 9, at 214–217.

[40] Id., at 222–226.

[41] Id. at 210.

[42] Peter Haggenmacher, “Grotius and Gentili: A Reassessment of Thomas E. Holland’s Inaugural Lecture,” in Hugo Grotius and International Relations (Hedley Bull, Benedict Kingsbury & Adam Roberts eds., 1990), 156-157.

[43] Id.

[44] Van der Molen, supra note 35, at 319.

[45] See Peter Schroeder, “Vitoria, Gentili, Bodin: Sovereignty and the Law of Nations,” inThe Roman Foundations of the Law of Nationssupra note 9, at 163, citing Benedict Kingsbury.

[46] Hugo Grotius, De Jure Belli ac Pacis Libri Tres (Francis Kelsey trans., The Classics of International Law, James Brown Scott ed. Oxford, 1925) available at

[47] Anthony Pagden, Gentili, “Vitoria, and the Fabrication of a ‘Natural Law of Nations’,”in The Roman Foundation of the Law of Nations, supra note 9 at 340.

[48] Diego Panizza, “Alberico Gentili’s De Armis Romanis,” in The Roman Foundation of the Law of Nations, supra note 9, at 57–58.

[49] Peter Schröder, “Vitoria, Gentili, Bodin: Sovereignty and the Law of Nations,” in The Roman Foundation of the Law of Nations, supra note 9at 165–167.


For Further Reading

Alberico Gentili,  De Iure Belli Libri Tres, translated by John C. Rolfe, with an introduction by Coleman Phillipson (Oxford: Clarendon Press, 1933)

Anthony Padgen, The Burden of Empires: 1539 to the Present (Cambridge University Press, March 2015)

Bardo Fassbender & Anne Peters eds., The Oxford Handbook of the History of International Law (Oxford: Oxford Univ. Press 2012)

Benedict Kingsbury & Benjamin Straumann, eds, The Roman Foundations of the Law of Nations: Alberico Gentili and the Justice of Empire (Oxford: Oxford University Press, 2011).

Diego Panizza, Alberico Gentili, Giurista Ideologo Nell’Inghilterra Elisabettiana (Padova: 1981)

Gezina van der Molen, Alberico Gentili and the Development of International Law: His Life Work and Times (Leyden Sijthoff 1968)

Hedley Bull, Benedict Kingsbury, and Adam Roberts (eds), Hugo Grotius and International Relations (Oxford University Press, 2003)

Martin Loughlin, Foundations of Public Law (Oxford: Oxford University Press, 2010).