The traceless disappearance of the Holy Roman Empire from the map and the minds of nineteenth-century Germany was until recently a pervasive historiographical trope. Revisionist scholarship has since uncovered the empire’s modern afterlife as a model for federative political order and archetype of the greater German (großdeutsche) nation. This article identifies a different type of legacy, by examining the empire’s role in shaping the constitutional configuration of an individual successor state: Prussia. In a debate over Prussia’s unwritten historical constitution unfolding in the 1840s, narratives of the empire’s constitutional history became the basis on which the juridical structure of the kingdom’s sovereignty was negotiated by jurists and political actors. These included, among others, King Frederick William IV and his brother William, the leaders of the German historical school of jurisprudence Savigny and Eichhorn and the Prussian statesman Kamptz. The article contrasts two rival interpretations of the imperial legacy: a teleological narrative focusing on the evolution of state sovereignty within the imperial constitution and a genealogical narrative highlighting the origins of sovereignty as a hereditary fiefdom. In doing so, it questions the rigid distinction that historians have drawn between the empire and the statehood that replaced it in 1806.