The Coastal Seas in International Law: Contextualising Grotius’s De iure belli ac pacis

Abstract This article reconsiders Hugo Grotius’s contribution to the law of the sea by shifting the focus from Mare liberum (1609) to the more nuanced arguments of De iure belli ac pacis (1625). While often portrayed as the chief advocate of the freedom of the seas, his later work reveals a more complex position: without abandoning the principle of free navigation on the high seas, he acknowledged that coastal states might, under specific conditions, assert exclusive rights over adjacent waters. Situating Grotius within a longue durée framework, the article traces the evolution of coastal jurisdiction from medieval practices in the Low Countries and beyond, through early modern diplomatic disputes over fishing rights and neutral waters. In particular, Grotius outlined the distinction between maritime dominium and imperium , hinting at the fact that exclusive rights at sea derived from either physical proximity to the coast or effective control. The discussion then extends to Cornelius van Bynkershoek’s De dominio maris dissertatio (1702), which developed the so-called cannon-shot rule as pragmatic compromise between maritime sovereignty and the freedom of the seas. By contextualising Grotius’s contribution, the article underscores the negotiated and dynamic character of the law of the sea.