The aim of this article is to analyse the essential methodological function of history in expanding the horizons of the study and practice of international law. Furthermore, showing that to reach a deeper understanding of international law it is not only necessary to use history in general, and the history of international law in particular, but also what Marc Bloch called the craft of the historian. The analysis will be conducted on two parallel levels. The first one focused on the work of historians and aimed at understanding methodologies of historical inquiry and techniques of writing and argumentation. This will be done by "dissecting" pieces of particularly relevant scholarly work by authors such as Eric Williams, John Gallagher and Ronald Robinson. The second one, instead, will analyse the transposition of those techniques and methodologies across the disciplinary border, into international law, and consider the (beneficial) effects of such transposition by looking at concrete models of how the craft of the historian can be successfully integrated in both international legal scholarship (José-Manuel Barreto) and international judicial-legal reasoning (Christopher Weeramantry).