Abstract: The transformation of Europe from the medieval imperial system to the sovereign state system is a major event that has a profound impact on European and world politics. However, how this transformation is manifested in the field of law has not been studied in depth. The study on the “public” dimension of Roman Law is largely absent in legal research and the study of history does not touch the issue of law, thus forming a theoretical gap. By exploring the tradition of European Roman law interpretation, this paper presents the legal logic of two political models, European medieval empire based on feudalism and modern sovereign state, confirms the key role of jurist in Europe political transformation. By revealing the Roman Law origin of European sovereignty concept, it shows the important position of Roman law in European public law research tradition.