Some commercial rules might appear universal and almost atemporal. This appearance has sometimes favoured theories on global commercial practices, and especially the idea of a universal lex mercatoria developed by traders for traders without external influences. While the pitfalls of such an approach have been shown time and again in the literature, this has had limited effect on the advocates of such an idea. Perhaps a more fruitful approach could be trying to distinguish general principles from their practical application in pre-modern commerce. Blurring them together has favoured general narratives of universal rules. Perhaps more importantly, it has also sidelined the underlying issue of why some general principles are indeed attested almost universally. If general principles may pass unscathed across time, the practical rules deriving from those principles usually do not. Those rules need to be interpreted within their historical and economic context: this may help to make sense of their diversity and account for their variety.
When looking at the environment in which a rule was applied, however, there is often a tendency to discount the legal features of that environment. After a period in which customary commercial rules remained largely oral, they were written down. This process is often neglected in the scholarly analysis of the rules. Straightforward as it might seem, however, the simple fact that an oral rule was written down did leave profound marks on the rule and its working. Moreover, once written down those rules often began to be studied and interpreted by learned jurists, who looked at them through the lens of legal concepts often quite alien to the environment in which the rules were originally produced. Roman law is a case in point, as during the early-modern period being a university-trained jurist by and large meant having studied Roman law. The progressive re-writing of medieval rules and their inclusion in compilations of growing length and complexity often led to a revision of those same rules, in which Roman law concepts acquired an importance they often did not possess before. The study of those commercial rules, therefore, must take into account both the social, economic and technological circumstances in which they were produced and the intellectual and legal environment in which they were later interpreted and re-fashioned. If this second kind of environment is discounted, it may stand in the way of a better understanding of those very rules. One of the reasons that suggest taking this environment into account is not usually discussed, as it is somewhat counter-intuitive. It was not easy for jurists imbued with Roman law doctrines to leave them aside – even when they wanted to. This was the case especially in those parts of Europe whose legal character was defined by Roman law: there, to reach a solution in line with non-Roman commercial practice, some Roman law reasoning had to be employed all the same.
This article does not offer a methodological analysis that should then be applied to the sources. Rather, it shows those methodological problems as they emerge from the study of the sources, which will be both the point of departure and of arrival in the analysis. To do so, an ancient legal institution was chosen: that of general average. General average is a voluntary sacrifice of part of the cargo (and/or of part of the ship) made during navigation in order to save the rest. It is a principle that has amply withstood the test of time, and that looks apparently simple, and deceptively consistent. The challenges of seafaring are unquestionably similar across space, and – despite technological advancements – time. A storm might break out during a voyage between Izmir and Venice just as much as it could while sailing from Riga towards Lübeck, or from Bordeaux to Plymouth. In each case, if cargo was jettisoned or some masts were cut to lighten the ship, the damage had to be spread among all parties involved. The way in which the damage was apportioned, however, could vary significantly, both because of different possible ways to evaluate what was left on board, and because of the different ways in which the shipmaster could – or could not – contribute. Rules on general average are often of customary nature, and initially were often oral. When written down, however, their meaning began to change. It was no longer a question of recalling an oral tradition, but of interpreting a written text. Commercial compilations, in turn, could easily be amended, and even merged together. The result would often affect their content even further. To illustrate the point, the example will be made of the requirement of the merchants’ consent to jettison their goods – a requirement which maritime compilations increasingly emphasised, to the point of rendering their provisions hardly applicable in practice. When those same compilations began to be interpreted using legal categories extraneous to the medieval and early-modern mercantile tradition (i.e., Roman law) the result was even more detached from practice – at least on a formal level.

This article was long in the making. Perceiving its complexity, I tried hard to sideline general average while working on early-modern English maritime insurance: dealing with it would have required another book. When I thought that I had escaped the danger, I received an offer by Maria Fusaro to take part in her ambitious new project on early-modern general average (ERC Grant agreement No. 724544: ‘AveTransRisk – Average, Transaction Costs and Risk Management during the First Globalization (Sixteenth-Eighteenth Centuries)’). The project was too interesting to refuse. Thus, despite all my precautions to sideline general average, general average caught up with me. During the project, I had the privilege of working with many excellent scholars and friends, Andrea Addobbati, Giovanni Ceccarelli, Dave De ruysscher, Gijs Dreijer, Jake Dyble, Maria Fusaro, Marta Garcia Garralon, Sabine Go, Antonio Iodice, Luisa Piccinno, Giada Pizzoni, Ana Maria Rivera Medina, Lewis Wade and Ian Wellaway, to whom I owe a happy debt of gratitude. A preliminary draft of the article was inflicted upon the participants in the 2024 Summer School of International Research Network PHEDRA (‘Pour une Histoire Européenne du DRoit des Affaires’) at La Rábida in Spain, and I am very grateful for the comments received. Finally, special thanks are due to Maria Fusaro for patiently reading the typescript, to the anonymous Reviewers for their useful suggestions and helpful remarks, and to Martin Kurz for his kind help during the editorial process. This study was completed with the support of the Leverhulme Trust (PLP-2020-361), which I gratefully acknowledge.