For fifty years now, historians have had at their disposal a coherent account of the law of arms applicable in the Court of the Constable and Marshal to cases concerned with the dividing of spoils and the ransoming of prisoners taken in wars.1 Disputes over these matters were resolved by reference to any contracts formed between the parties involved, failing which to any regulations issued in relation to the particular conflicts in which they fought, failing which to more general regulations or the customs of warfare. At the more general level especially, the law of arms had an international flavour, for the regulations introduced in one place were often influenced by those already in force elsewhere, and the communities that considered themselves obliged to conform to customary usages were not always nationally defined. It was of course important for the decisions delivered in the courts of one place to appear acceptable in the other places from which those despoiled or imprisoned came, and it was partly to this end that the practice of military tribunals was rationalised in terms of the legal theory expounded in broadly similar terms in universities throughout Europe. The learned doctrine of the law schools provided a framework of legitimacy within which courts in different parts of Europe were able to fashion versions of the law of arms that could be expected to receive recognition elsewhere. It follows that to understand the law of arms properly required – and still requires – familiarity with academic theory as well as forensic practice.5 It was not without cause that advice was taken on the application of the law of arms from ‘doctors of law’ or ‘iurisperiti’, a cadre of experts in the civil and canon laws whose advice was relied on in the specialised courts of the Constable and Marshal, the Admiral, and certain other officials.