On January 17, 2019, France announced that it was creating a task force for the restitution of Nazi looted artworks in compliance with the EU Parliament Resolution to Identify and Recover Looted Art. The country’s president, Emmanuel Macron, has also commissioned a study aimed to repatriate artworks stolen years ago from France’s former colonies. Neither of these recent developments is particularly surprising; today, the principle of restitution of stolen, illegally traded, imported or exported art has been codified in many international law treaties to the point of becoming a principle of customary international law (Barakat case).
However, this principle is not old in legal history. It was officially introduced by the First Protocol to The Hague Convention for the Protection of Cultural Property in the Event of Armed Conflict (1954), jointly drafted by the Italian delegation and UNIDROIT. The provision regarding the restitution was purposefully left out of the core text of the agreement because it was still subject of strong opposition. The restitution principle comes from the consolidation of a negative principle: the negation of the prize right. The abandon of the right of booty vested in the winning army over the occupied state was outlined for the first time in the so-called Martens Clause, in The Hague Convention II, of 29 July 1899. The clause accorded a sort of privileged status to certain categories of goods in wartime including national cultural property. Such principle was later on reproduced in the Annex Regulation to the 1907 Hague Convention.
However, there was a time when the prize right—the right that the winning party held to deprive the defeated party of its men, its wealth and its national pride—was recognized in international law. Back in the time, ancient Romans allowed predation in tempore belli (wartime). Jurists like Gaius, Ulpianus, and Marcianus referred to the ius praedae (prize right) as a legitimate institution under the Roman law of nations—the so-called ius gentium. In the Institutiones, Marcianus considers war prisoners as belonging to Roman armies either under the ius civile (private law) or the ius gentium. The exercise of the ius praedae was possible only through a bellum iustum—namely, a just, fairly declared war, which was considered a iusta causa (right cause) to legitimate the acquisition of possession over men and goods. The act of plundering (direptio) was an actual method of acquiring ownership of res hostium—namely, the enemies’ movables. Some scholars consider the booty as acquired, ipso iure, by the Roman Republic (then Empire); some others consider it as becoming soldiers’ private property gained through occupatio (a method to acquire ownership); still others believe that the booty was at the mercy of generals until it was paid into government treasury (praedam in aerarium referre) or divided among the veterans (praeda militi concedere). On the contrary, predations in bellum nefandum (unfair war) and meaningless predations against Roman citizens were ascribed as crimes and generally condemned to restitution.
Once the bellum iustum was over, goods and prisoners were occasionally sold by the general on the battleground, or by the quaestor (public officer) in Rome. The sales used for those transactions were ancestors of today’s auction sales, named venditio sub corona and venditio sub hasta. The sub corona was particularly used for the sale of slaves and it might owe its name to the crown-like headgears (corona) worn by the prisoners.
The principle of international restitution of public and private property, established by the law of the 1970 UNESCO Convention and 1995 UNIDROIT Convention, also has roots in Roman times. Cicero, in his In Verrem, refers to the restitution of cultural property to the Sicilians from the Carthaginians, as a socio-cultural phenomenon because a legally binding mechanism was absent at that time. Titus Livius writes that after the Third Punic War, Scipio “returned the greater part of the spoils” and seemed also to have ordered a general search of the plunder from Carthage for items taken in the past from Sicilians for the purpose of restoration. The same concept of bellum iustum was recalled in the fifth century by Saint Augustin in De Verbum Domini and, later on, reconsidered by Saint Thomas Aquinas who again justified war booty when gained fighting a just war.
The first attempt to stop the practice of war booty came from the Holy See, right after the so-called Sack of Rome by the Landsknechts in 1527. After having blessed reiterated spoliations of the Holy Land during the Crusades, when the pillage of Rome occurred, the Pope strongly stood against the brutality of despoliations inflicted by occupying soldiers to the national treasury. The Pope passed a rule that declared cultural property in the possession of the Church as res sacrae extra commercium (sacred not-tradable objects). However, despite this progress, over a century later Alberico Gentili, an Italian jurist, had no hesitation in justifying the war-booty and the condition of slavery as fair provisions under the law of nations. Some years later, his philosophical heir, Hugo Grotius, in De jure belli ac pacis and De Jure Praedae, represented the ideal of bellum iustum and reaffirmed the prize-right in international law (over private and public cultural goods).
The first faint signs of change came almost three centuries later. In the late 18th century, Napoleon’s successful campaigns brought to France a massive number of works of art belonging to national treasuries and private estates. According to the legend, the masterpieces were singled out and listed by Dominique Vivant Denon, l’oeil de Napoléon (Napoleon’s eye), following the Directoir’s orders. At that time, the French architect and philosopher, Antoine-Chrysostome Quatremère de Quincy, poured out all of his frustrations and concerns regarding Bonaparte’s widespread lootings and absence of respect towards foreign national and private property in his Letters to Miranda. When the Congress of Vienna opened its doors (September 1814 – June 1815), the necessity to preserve an equilibrium led to the restoration of the status quo ante bellum and to the restitution of the majority of the rich war-booty acquired manu militari. Although significant results were achieved at the beginning of the 18th century, yet there was no written law to enforce or soft law to recall: there was only a “strong moral consensus against war-booty in which scholars stressed their ideas of natural law, humanity, and the strict separation of private and public property in time of war” (Frigo M.). It was not until the twentieth century, with the adoption of the so-called Cultural Conventions, that the prize right disappeared and the restitution right began its ascension.
 The bellum nefandum was an “unfair war”, declared against the ius fetiale. Bellum iustum was an officially declared war, by the sacerdotes fetiales with the indictio belli cermony and the taking of the auspices. Livy 1,32,5-14.
 M. Talamanca, Contributi allo Studio delle Vendite all’Asta nel Mondo Classico, Fascicolo 2, Serie VII, Volume VI, Atti della Accademia Nazionale dei Lincei (1954).