The rediscovery of the Roman jus gentium and the post 1945 international order

Abstract

The main query of this contribution concerns the circumstances and conditions under which the concept of jus gentium as it existed in Roman law is included in or excluded from the historical canon of international law. Paradoxically, according to the major twentieth-century handbooks on the history of international law the term ‘law of nations’ derives from the Latin jus gentium. However, historians of international law tend to indicate the jus gentium does not amount to any ‘international law’ in the modern sense. The contribution argues that the idea of the Roman jus gentium as equivalent to our modern international law was rediscovered in the 1930s and 1940s, first by a group of leading Roman law scholars who were ousted from Germany by the Nazi regime, and second by a larger group of thinkers and academics they came into contact with in their new academic surroundings. The reason for this rediscovery is a change in the definition of ‘international law’ especially beyond legal positivism, to encompass two qualities the Nazis despised: individualism and universalism. The purpose of the contribution is to show an instance of a change in canon due to the political circumstances, one with consequences for the formation of actual institutions in international law.

1. Introduction

Is there room in the historical canon of international law for classical Antiquity? The question is difficult to answer, because it not only depends on the existence of the notion in Antiquity itself, but also on what constitutes the definition of ‘international law’ according to who poses it. The definition of ‘international law’ in general seems contingent on political and societal circumstances and considerations, thus its history appears to change depending on the time period in which the notion is defined. This article aims to examine a singular instance of such a change in definition, namely the period between the 1930s and 1950s in Western Europe and the United States in which there was an emergence of refugee scholarship among legal scholars who were forcibly displaced by the Nazi regime in Germany. The argument is centred around a peculiar notion in classical Antiquity, namely the jus gentium as it occurred in Roman law. This notion will be defined more in depth below. This article claims that due to these political circumstances the Roman notion of jus gentium came to be included in the historical canon where before it had not been. The reason for this is certain specific characteristics that the Roman notion of jus gentium had, or were ascribed to this notion, by the refugee scholars in question.

To demonstrate this wide-ranging and far from singular process of reinvention, first the Roman notion of the jus gentium will be traced in various prominent handbooks and scholarly works on the history of international law from the nineteenth and twentieth centuries. Next, the presence in these handbooks will be contrasted with the perspective on the notion of Roman law scholarship itself in the same period. It seems that this perspective led to a particular form of taking up the Roman notion of jus gentium among legal scholars forcibly displaced to the United States. The scholars in question studied and developed private international law, taking up the private law dimension of the Roman jus gentium to their benefit. I will indicate this perspective as the ‘individualist’ perspective. Subsequently, other aspects of the Roman concept came to be emphasized, such as its foundation in the Roman idea of natural law. The Roman jurists had already connected the notions of jus gentium and jus naturale through their supposed shared respective practical and theoretical universal validity, hence this perspective will be designated as the ‘universalist’ perspective. After the end of the Second World War the impact of the rediscovery of the Roman notion of the jus gentium is felt most clearly when both perspectives came together in the search for new types of international law, aiming to realize its universal and individualist ambitions. Lastly, via a treatment in various post-war handbooks, the Roman notion of jus gentium was folded back into the traditional narrative, nowadays usually obscured as a ‘pre-history’ or ‘precursor’ of modern international law.

It is difficult to provide a singular definition of the Roman concept of jus gentium, as there is a multitude of definitions already in Roman Antiquity itself. ¹ To be clear, whereas the term literally means ‘law of peoples’, the notion of jus gentium differs structurally from our modern idea of ‘international law’, although our modern concept is ultimately derived from it. ² Two complexes of definitions need, however, to be distinguished: first the Roman philosophical one as primarily related by Cicero meaning a law valid for all peoples of which the jus civile or law for Roman citizens is a part, and which is a reflection of natural law in the Stoic sense. ³ The meaning of this philosophical understanding of the jus gentium had changed in the works of the jurists of the imperial period about two hundred years later, Gaius above all, who completely separate the jus gentium and jus civile, perceiving the former as the common law valid in the Roman Empire beyond Roman citizenship. ⁴ The second complex of definitions is even more directly pertinent to our problem, namely the difference in meaning between the jus gentium as a ‘public international law’, including the law of war and treaties, and the jus gentium as a more-or-less ‘private international law’ (taking into account the differences in periodization for instance between Cicero and Gaius) governing the private relations between Roman citizens and non-citizens either inside or outside the Roman territory in a number of specific legal contexts. ⁵ Although the definition is somewhat fluid, what does interconnect the various meanings is an idea of the jus gentium as a shared or common law, with the complex process of the reception of Roman legal texts from the Middle Ages onwards and their constant rediscovery and reinvention explaining how it could be at the root of our modern thinking about international law.

2. The Roman jus gentium beyond the canon of international law

Up until the early twentieth century, the history of international law starts with the Dutch scholar Hugo Grotius (1583–1645) with whom we can ascertain a move from ‘not international law’ to ‘international law’. For example, in Lassa Oppenheim’s fundamental handbook, the absence of international law in Antiquity is made very explicit, the paragraph in question in the part on Peace being titled ‘No law of nations in Antiquity’. ⁶ Although the Romans then did have legal rules for its foreign relations, especially war and treaties, the main issue concerning the existence of an early form of international law in this period seems to be the superstructure of the Empire on the one hand and the lack of ‘civilised states’ outside the Roman territory on the other. ⁷ In Arthur Nussbaum’s Concise History we encounter more elaborate discussions of the problem of international law in Antiquity in this context, distinguishing between the ancient orient, Greece and Rome, and mentioning the earliest instance of a treaty in 3100 BCE between the city-states of Lagash and Umma. ⁸ On Roman legal thought Nussbaum is relatively expansive, starting with the function of priests (fetiales) in the Republic with respect to the laws of war, and continuing with the concept of surrender (deditio), the treaty system, envoys, the term jus gentium, forms of legal protection for non-citizens, notions of natural law, and slavery. ⁹ There does not, however, seem to be a clear relation between the practice of international law, and the concepts of jus gentium and jus naturale. According to Nussbaum especially the jus naturale all too often formed an ‘invented tradition’ on which new legal notions could be based. ¹⁰ Sometime later, in his Epochs of International Law Wilhelm Grewe even upholds a fairly positive image of the existence of some forms of international law in Antiquity. However, the relevant section only counts four pages and is not enough to warrant a designation of any period in Antiquity as a separate epoch. ¹¹ Also in more recent handbooks, a history of international law commences in the fifteenth or sixteenth century, either leaving Antiquity unmentioned completely ¹² or discussing primarily Roman legal notions as a basis for its later development. ¹³ In general, in writing the history of international law Antiquity is given fairly short shrift and usually taken as a ‘pre-history’ on the basis of which later more accomplished versions of international law would be formed. ¹⁴

To understand the idea of the jus gentium from a standpoint of Roman law scholarship beyond the handbook-narrative of the history of international law, a brief introduction has to be provided, mainly with respect to German-speaking studies on the matter. In Germany in the late nineteenth and early twentieth centuries the legal positivist concept of public international law was mitigated by concurrent more naturalist and philosophical considerations. The question that remains pertinent even for the twenty-first century is the measure in which basic notions of ‘modern’ international law, treaties, immunities, rules for warfare et cetera, relate to ancient more abstract and philosophical concepts such as dikaion koinon/jus gentium and dikaion fysikon/jus naturale, if at all. The scholar who has given the most complete treatment is Moritz Voigt (1826–1905), professor of Roman law at Leipzig. ¹⁵ Just to indicate how difficult and intricate the problem is, the subject took him four volumes, comprising several thousand pages. Voigt’s work remains by-and-large unknown outside of a specialist readership. In his second volume on the relation between the jus gentium and the jus civile Voigt recognizes a twofold conception of the law of nations among the Romans: first by virtue of its content, as a ‘law of war and peace’, and second based on its subject, the ‘nation’ (gens) rather than the people or the tribe. Moreover, in the Roman conception the jus gentium encompassed all nations, not just those with specific political or ethnic traits, and even more astounding, it concerned all free men equally. ¹⁶ As such, Voigt discusses the content and (primarily private law) scope of the jus gentium from the conceptual to everyday legal practice in the remainder of the volume in three periods: the first until Cicero, the second between Cicero and the third century CE, and the third until the reign of the Eastern Roman Emperor Justinian in the sixth century CE. ¹⁷ The main difference between the first and the second periods is the measure in which the Romans exerted control over the Mediterranean from the first century BCE onwards, allowing for a jus gentium that was both universal in concept and practical in scope. ¹⁸

Building on Voigt’s work, in 1891 the Roman law scholar Ludwig Mitteis (1859–1921) took up the discussion on the relation between what he termed ‘Reichsrecht’, the central law of the Roman Empire, and ‘Volksrecht’, local and municipal laws. ¹⁹ Not only did he advance a strong distinction between the development of this relation in the Western and Eastern provinces of the Empire, according to Mitteis the local laws in the Eastern provinces even managed to some degree to influence the Reichsrecht. ²⁰ Greek law is presented as a unified law with a general development and a universal tendency. ²¹ Under Greek law treaties offering legal assistance guaranteed a measure of mutual legal protection specifically in the context of trade in dedicated peregrine courts (Fremdengerichte). In a similar manner as would happen later as a result of the legal practice of the Roman peregrine praetor shaping a jus gentium, these peregrine courts delivered their own version of an ‘international law’, one that even surpassed the ‘selfish economic’ one of the Romans. ²² With the work of Mitteis, a renewed interest emerged in ancient law beyond that of Rome, especially in the context of what was termed ‘ancient legal history’ (Antike Rechtsgeschichte).

In a 1927 programmatic document, an Austrian scholar of Mitteis called Leopold Wenger (1874–1953) argued that the emphasis in legal history was to be shifted from Roman law alone to a wider perspective, including for example the legal orders of Greece and Egypt. ²³ The shift away from Roman law concerned the jus gentium in particular, since Wenger saw this as a law expressing Roman hegemony first and foremost. ²⁴ Through this method, a cultural history of Antiquity as a whole can be written, with the study of ancient law as a sub-discipline of classical studies, however one that remains focused on law and the state. ²⁵ Although their conclusions differed fundamentally, ²⁶ there is an interesting interplay in both Mitteis and Wenger in what constitutes as ‘national’ and ‘international’ law in Antiquity, going much beyond the Roman conception of jus gentium as it was prevalent in the handbooks of international law of the time alone. After Voigt, Mitteis and Wenger the discussion among scholars of ancient law has remained centred on three complexes of problems: the meaning and development of the notion of dikaion koinon/jus gentium, the existence of a ‘conflict of laws’ primarily between Roman and other ancient legal orders, and the scope of legal remedies afforded to non-citizens in any legal order in Antiquity. ²⁷ These three complexes of problems seem interrelated, although the exact relation remains unclear and disputed to this day.

In the same year as Wenger’s programmatic work, two publications on international law and its historical precursors saw the light of day. These adopted a completely separate perspective from Wenger’s and ultimately came to profoundly shape the subsequent trajectory in the field. Following Voigt, the French Romanist Felix Senn emphasized the importance of the link between the jus gentium and the jus naturale in ancient Rome and even its centrality in Roman legal thinking, the jus gentium being the natural law proper to mankind as opposed to the natural law that man and animal have in common. In this, the jus gentium indicated an application of natural law in legal practice. ²⁸ Senn’s work coincided with a small revival of natural law thinking in international law particularly among scholars such as Alfred Verdross and James Brown Scott, the latter championing the role of the Spanish late Scholastics who similarly wrote extensively on the link between jus naturale and jus gentium. ²⁹ Certainly, the First World War and its aftermath contributed to a renewed attention for possible moral foundations of international law, and vice-versa whether international law could function as a conduit by means of which moral principles or natural law could be realized.

Although the perspective is completely different, a similar premise underlies Hersch Lauterpacht’s 1927 dissertation at the London School of Economics on Private Law Analogies and the Sources of International Law. Focused on contemporary black-letter-international law but framed by a historical-legal theoretical framework, Lauterpacht demonstrates the manner in which private law arguments and notions are used in an international context. Specifically, Lauterpacht equates domestic private law and Roman law, or at least legal concepts derived from the Civil law tradition, such as prescription in land occupation. ³⁰ The notion of jus gentium as a universal private law based on comparative jurisprudence is excluded from the historical-theoretical framework. ³¹ Nevertheless, Lauterpacht queries the role of Roman law and the legal concepts inherent in it in the historical development of international law. It has to be taken into account that the dividing line between international and private law in Roman law is vague at best considering the jus gentium encompassed what we would now designate as both public and private (international) legal notions. The importance of Roman law for international law in the nineteenth century is stressed primarily based on a variety of English and American scholars, ³² whereas the Germans tended more towards positivism, rejecting recourses to analogies with private law. ³³

3. Roman law and 1930s and 1940s refugee scholarship

The works of Mitteis, Wenger, Senn, and Lauterpacht set the scene for a peculiar development in legal history. Mitteis had passed away in 1921. Wenger, Senn and Lauterpacht were all personally affected by the advent of fascism and the Second World War in different ways. Under Nazism the study of Roman law was precarious because of Article 19 of the NSDAP programme, preferring a German common law over Roman law as the latter ‘served a materialistic world order’. Moreover, many prominent Roman law scholars were perceived by the Nazis as having undesirable political views or a Jewish or otherwise non-Aryan family background, and were fairly rapidly sidelined. Usually this resulted in their forced displacement, for example to the UK and the US. Neither country has a Roman or Civil law tradition that is even remotely comparable to the German-speaking one. Thus, scholars that were traditionally trained in Roman law needed to adapt their scholarship simply to find employment in the new academic context. ³⁴ This happened in various different ways, all pertinent to a rediscovery of the Roman concept of the jus gentium in the 1930s and 1940s.

The first manner in which Roman law was adopted to fit a new academic context in the 1930s is due to predominantly shared interests of particularly the erstwhile scholars of Ludwig Mitteis and a section of Anglophone legal scholars in Roman law as a basis for comparative law, the conflict of laws, and private international law. ³⁵ As such, with its focus on the relation between various ancient legal systems some of the scholars of Mitteis ended up in fertile ground, enjoying relatively successful careers even after their forced displacement to the US. Primary among them is the Austrian-American legal scholar Ernst Rabel (1874–1955) who was forced to leave the University of Berlin soon after the Nazi take-over, as well as his pupil Max Rheinstein (1899–1977), but of course the group was much larger. ³⁶ In his comparative method, Rabel appears to develop a universal system of (private) law by means of the creation and application of conflict rules. As such, even in his 1930s works on modern (US) law his Romanist background shines through often. ³⁷ According to Stagl particularly in the law of sale Rabel takes inspiration from the Roman jus gentium as a historical example, not so much its content (although it could be said the Roman law of sale was a part of the jus gentium par excellence), but more the manner in which it came into being. Briefly put, first similarities between various legal systems result in more-or-less universal rules on an international level; second, these rules are implemented in the domestic legal systems again, ensuring a proper enforcement not because of a ‘world-state’ but simply because it is the result of ‘juristic insight’. ³⁸

In and of itself, the concept of jus gentium is not that pertinent or interesting for dogmatic research into Roman law: the structural aspects of the legal notions are much more relevant than for example the reason why they came into being. Also influenced by the rise of antike Rechtsgeschichte, the study of the jus gentium in Germany thus primarily became a matter for ancient historians, not lawyers. ³⁹ Overseas, however, the question was asked whether by placing the concept within its historical context the Roman idea of jus gentium could be employed to solve contemporary legal problems in private law ⁴⁰ and in international law, the latter for example by re-examining moral grounds for entering into a just war. ⁴¹ The main exponent of a legal realist perspective on the Roman concept of jus gentium may well be the legal theorist at Berkeley Max Radin (1880–1950), who composed an encyclopedia article on the topic, and lectured at the Romanist Riccobono seminar during his presidency at the Catholic University at Washington, DC. ⁴² As such, Radin fits well within the post-war development of presenting Roman law in general or the Roman conception of jus gentium as a precursor to particular institutional developments, above all the formulation of human rights, the creation of international organizations such as the UN, and the erection and construction of the Nuremberg Trials. ⁴³

Conceptually, it is interesting to note that the Roman jurists did not use the term jus gentium before the time of the Emperor Hadrian in the second century CE, when the Classical period of Roman law and deep-rooted contacts on trade and other matters of what we would now term international law had long since been established. ⁴⁴ Thus, from Roman legal scholarship there emerged a gap between the concept of jus gentium and the practice of trade and communication between peoples. Moreover, it is the Roman republic that tended to be viewed as the more inclusive society. The empire on the other hand was generally seen as despotic and absolutist, an idea that compared poorly to the cosmopolitan character of the notion of jus gentium among the jurists emerging only in the second century CE. ⁴⁵ Apart from the discussion on private international law, the second manner in which the jus gentium played a part in 1930s and 1940s legal scholarship is the conceptual relation between ‘international law’ and ‘natural law’. In the light of their intellectual backgrounds, steeped in legal positivism and all too aware of Nazi legal theory, refugee scholars took up the question of natural law. ⁴⁶ Rather than a full-scale repudiation of natural law, the political scientist Ernst Fraenkel (1898–1975) argues that the Nazis upheld a ‘communal natural law’ over a ‘societal natural law’, detailing the differences in a separate chapter of his Dual State. As such, whereas communal natural law is limited to the community to which it owes its existence, thus making the only international law that which is written, societal natural law is valid for the whole world. ‘Jus gentium as natural law is in contrast with jus civile as positive law’. ⁴⁷ Of course, the universalist tendencies of the Roman concept of jus gentium particularly in its close relation to the jus naturale were widely noted before, during and after the war.

A peculiarity of the jus gentium is not only its purported universalism, but also the fact that it could be invoked by individuals – Romans and non-Romans – before a specialized magistrate. Cicero has presented the jus gentium as a realization of natural law – a law that contrary to natural law in the Roman conception actually was enforced just like the jus civile. ⁴⁸ It is this individualism that was seen as inherent in Roman law in first instance by the Nazis, as well as a quality they abhorred specifically in the eighteenth century conception of natural law. ⁴⁹ Therefore, it is no surprise that among refugee scholars the individualist tendencies in Roman law were emphasized. ⁵⁰ Primary among them is Lauterpacht, building on his 1927 work in the course of the 1930s in developing individualist conceptions of human rights. ⁵¹ In 1943, he would provide his concept with the Roman jus naturale and jus gentium on the same footing, presenting jus gentium as the positive law component of natural law, ⁵² although in his view any fundamental relation between international law and human rights only really commences in the theory of Grotius. This development seems to be peculiar to international lawyers, as the historical narrative of the burgeoning discipline of international relations tends to start with Thucydides, with scholars such as Hans Morgenthau critiquing the usage of Roman law in an international law context. ⁵³

Generally, the Roman concept of jus gentium demonstrated it was possible to have a more or less universal set of rules, relatively independent from a centralized legislator, coupled with concrete and accessible procedures leading to effective forms of legal protection beyond and even against a hegemonic ‘state’. Moreover, the concept inherently combined two qualities of a legal system the Nazis explicitly had decried, ‘individualism’ and ‘universality’. In this sense, the rediscovery of the Roman concept of jus gentium pre-empts the revival of natural law after 1945. The renewed emphasis on the universalist tendencies is by no means unique to discussions of historical ideas of international law, jus gentium or other forms of law beyond the state, however, a connection to effective guaranteed concrete (private law) legal remedies and protections that the Roman notion offered was a novel addition. The Roman concept of jus gentium thus provided a fertile ground for early constructions of an international legal order that was expected to deal with the aftermath of the conflict, however unclear the scale of the atrocities still remained at this point in time.

4. Constructing a post-1945 international legal order

After 1945, there was at least a brief moment in which the individualizing and universalizing tendencies in the theory of international law in the broad sense – including political theory and international relations – may have contributed to the formation of practical institutions such as the Nuremberg tribunal and the Council of Europe. ⁵⁴ It is debatable how long this moment lasted, and how deep-rooted its influence was. Regardless, it was precisely because of the individualist/universalist convergence identified by the refugee scholars who drove the rediscovery of the jus gentium that the latter came to acquire so much traction in the making of the post-1945 international legal order. The ideas of the practical creation of the law of a ‘world-state’ and the jus gentium as the realization of an individually and universally styled natural law mainly in the realm of international law overlapped in several influential post-war theories. Interesting in this regard in particular are the early histories of human rights that included references to Roman law in general and the jus gentium specifically.

The first major work to address the Roman concept of jus gentium after the War is Gabrio Lombardi’s diptych on the concept and several legal notions termed as belonging to it by the Romans, both squarely within an Italian dogmatic tradition. ⁵⁵ However, erstwhile refugee scholars, but also several of those that had remained, reappraised the connection between jus gentium and jus naturale as crucial in the development of Roman legal thought and even ancient society. ⁵⁶ Beyond the academic, the primary influence of the Roman concept of jus gentium on the creation of post-war international institutions was exerted via a group of conservative Catholic scholars, who answered the call for the creation of a law beyond the state by reappraising Medieval thinking about natural law. ⁵⁷ The groundwork for this development was already laid out in the 1940s, with explicit references to the Roman link between jus gentium and jus naturale. Following Lauterpacht already in 1943, the connection between natural law and the specific Roman conception of jus gentium in a human rights context is made in 1945 by the French Catholic philosopher Jacques Maritain (1882–1973), who would later prove to be influential in the creation of the Universal Declaration of Human Rights. ⁵⁸ A year later the Belgian professor of international law and judge at the International Court of Justice Charles De Visscher (1884–1973) ⁵⁹ emphasizes that the jus gentium progressively extended the law over foreigners, evolving from a law valid outside the confines of the municipality to becoming a law that was seen as common to all mankind, one founded in natural reason at that. ⁶⁰ In later works, De Visscher, however, argued against creating individual claims under international law, opting instead for emphasizing the moral obligations of the states. ⁶¹

Apart from the Catholic personalists, the figure of Lauterpacht looms large over the post-war institutional debates surrounding the (historical) foundations of a new international legal order. ⁶² The historical narrative set out in 1943 is applied to the formulation of an International Bill of the Rights of Man in 1945, this time with an additional chapter on natural rights in British constitutional law. ⁶³ In the proposal, Lauterpacht does not so much problematize the universal character of the bill, but rather its enforcement. Interestingly, the enforcement envisioned is primarily one on the national level, i.e., via the judicial organs of the state. ⁶⁴ Beyond aiding in the development of the notion of human rights, among refugee scholars from German-speaking countries, the universalist characteristics of the Roman concept of jus gentium were at times employed in the service of teaching, as a notion providing easy access to the inner workings of the Civil law systems. ⁶⁵ Noteworthy is the presence of the term in the works of the political philosopher Hannah Arendt (1906–1975), especially when viewed from the perspective of her famous conception of a ‘right to have rights’, as the Roman notion of jus gentium seems to combine individual subjecthood to a law transcending the nation-state. ⁶⁶ Birmingham here refers to passages from Arendt’s 1966 Introduction into Politics and the 1968 work On Revolution, in which the Roman concept of jus gentium is not only seen as the basis for the Roman ‘political’ idea of law in general, ⁶⁷ but is also contrasted with the more limiting Greek view on ‘laws’ or nomoi. In defining the spaces between people, the Roman idea of law according to Arendt marked nothing less than the beginning of the Western world itself. ⁶⁸

As a consequence of its rediscovery among refugee scholars, there certainly was an increased attention for the Roman jus gentium as a precursor for modern international law in a number of 1940s handbooks. The first edition of Nussbaum’s Concise History dates from 1947. Moreover, in Germany two general works on the history of international law were published post-war, Geschichte des Völkerrechts by the classical philologist Georg Stadtmüller (1909–1985) and Völkerrecht composed by Ernst Reibstein (1901–1966), the first volumes of both works containing discussions of the jus gentium in Antiquity. ⁶⁹ Stadtmüller in his discussion explicitly links his perspective on the history (and reconstruction) of international law to the experiences during the War, the Nuremberg Trials, and the revival of natural law-thinking inspired by Radbruch. ⁷⁰ As such, he strongly emphasizes the link between the jus gentium as a law common to all peoples and the jus naturale as its moral foundation in the Roman empire, moreover relating it to the pax Romana securing the peaceful coexistence of all peoples in its territory. ⁷¹ However, where Stadtmüller provides an in depth-discussion of traditional forms of public international law, he decries the existence of both private international law and international criminal law in Roman Antiquity. ⁷² Reibstein’s work has a fundamentally different focus: the history of a (European) law of nations as an idea stemming from the development of the notion of jus gentium between the late-Classical imperial Roman jurists and the Early Church Fathers in first instance. ⁷³

The works of Stadtmüller and Reibstein form the introduction to a larger debate still going on that includes Nussbaum and Grewe, but also a more ‘maximalist’ perspective particularly of the historians of international law Wolfgang Preiser (1903–1997) and Karl-Heinz Ziegler, in which the Roman concept of jus gentium plays a crucial role. ⁷⁴ Reviewing Reibstein’s Völkerrecht, Wolfgang Preiser remarks that when the history of the law of nations is viewed from the perspective of the history of ideas, and when it is primarily the concept as it existed in the course of the Roman empire that is taken as containing its essential meaning, it is possible to view the Roman concept of jus gentium not just as a precursor, but as a starting point for a continuous later development of a European international law: ⁷⁵

Wieder befinde ich mich in grundsätzlicher Übereinstimmung mit dem Verf. wenn er, weit hinter die üblichen Ansätze zurückgreifend, die spätromische Kaiserzeit als Ausgangspunkt nimmt und die ihr zugrunde liegenden rechtlichen und staatlichen Anschauungen der vorchristlichen Antike als “Vorgeschichte des europäischen Völkerrechts” in fortlaufender Bezugnahme in seine Darstellung mit einschlieβt …. Natur- und Menschheitsrecht, Rechtfertigung des Krieges unter bestimmten Voraussetzungen, die ethischen Lehren des frühen Christentums und, durch dies vermittelt, des Alten Testaments- das alles Gehört zu den Grundlagen der europäischen Kultur allgemein, seiner rechtlichen Kultur im besonderen- nicht nur die Vorgeschichte, sondern ein integrierender Bestandteil der Geschichte des “europäischen” Völkerrechts.

Provided it is indeed specifically a ‘European’ law of nations as a singular idea stemming from the Roman jus gentium we are discussing, it is Preiser himself above all who to some degree at least reintroduced it to the larger handbook-narrative of international law, for example by Wilhelm Grewe who based his section in the 1984 Epochs on Antiquity primarily on Preiser’s scholarship. The idea in the review of Reibstein was elaborated on in several later publications, stressing the continuity of the idea of a European law of nations founded in Antiquity. ⁷⁶ In Preiser, however, as is the case in Grewe, the individualist private law connotation of the Roman jus gentium is noticeably absent, treating it exclusively in the sense of a public international law. ⁷⁷ Given its explicit ‘European’ character, one could say it has also lost its essential universal character. Therefore, to a large extent, the journey of the idea of a jus gentium ends up in the 1970s where it had started at the outset of the twentieth century, despite the consequences of the development of the idea in between.

5. Conclusion

The question of whether the Roman notion of jus gentium counts in any way as a precursor to modern international law – is ‘canonical’ in its history – needs to be distinguished from whether the Roman world knew any form of international law itself. Both questions are definitionally contingent, in the sense that the answer depends on which definition of jus gentium or international law is upheld and employed. When reasoning from a very positivist public international law outlook coupled with the jus gentium solely indicating the practical presence of a (Roman) legal rule in multiple legal orders, there really is ‘no international law in Antiquity’ in the guise of a jus gentium or otherwise. However, ideas of what constitutes a jus gentium in Antiquity alone (let alone in later time-periods) and what defines the law of nations or even international law are fluid, depending on the temporal and societal context in which they are formulated. Nevertheless, in the course of the 1930s and 1940s elements of the Roman notion of jus gentium seem to have been rediscovered, likely due to the legal upbringing and scholarly context of various refugee scholars in combination with the aversion of the Nazis to Roman law in general. In first instance, this element was the idea of the jus gentium as a common law among various ancient legal orders particularly in private law relations. The names of Ernst Rabel and his comparative law colleagues in the United States are most closely connected to this reinvention of the Roman notion of jus gentium.

The second strand of scholarship in which the Roman notion is rediscovered in the 1930s and 1940s stresses the connection between the jus gentium and the jus naturale made in both the ancient philosophical and legal texts. The idea is that the jus gentium realized a universal natural law with a strong moral content, in explicit contradiction with the communal natural law of the Nazis subordinate to principles of the common good. This article argues that these strands came together in a brief period after the Second World War to provide an intellectual basis for several crucial international law institutions, evidenced by explicit relations drawn between fundamental aspects of the Roman jus gentium and these institutions, namely human rights and the Nuremberg Trials. Briefly put, the jus gentium seems to have been singled out because it provided effective individual claims derived from a universal moral higher order beyond citizenship and (state)territory against the hegemonic legal order. As such, the workings of the jus gentium as far as it was possible to ascertain them were seen as it were as a laboratory in which a variety of newly minted post-war legal notions could be tested.

Via the works of Nussbaum, Stadtmüller, and Reibstein in the course of time the Roman notion of jus gentium was reincorporated into the ‘canon of international law’, being taken up by Preiser and consequently Grewe’s Epochs. However, in this ‘canonical’ context the jus gentium lost much of the meaning it has carried from the 1930s until the 1950s. The idea of effective individual (private law) claims in particular are lacking from the public law and state-based conception of Preiser and Grewe, as it really had been abandoned in the context of human rights claims under international law before. On the other hand, based on Rabel and his colleagues this idea was actually transferred to a modern comparative and private international law context. Nevertheless, with Nussbaum, it may be said that the Roman notion of jus gentium especially as connected to the jus naturale served as an invented tradition for a number of previously non-existent legal notions. Primary among them may be the concepts of human rights and crimes against humanity as developed by Lauterpacht. The interesting question to close this article thus becomes: if these previously inexistent legal notions nowadays form an important (and growing) part of international law, should the Roman jus gentium in the wider sense not be reincorporated in the canon of international law? Does and should the invention of new legal notions lead to changes in the canon of the legal context in which they are reinvented?