Abstract The caudillo strongman remains emblematic of Latin American authoritarianism, but scholarship has seldom reflected on the semantic shifts that this concept suffered over time and its implications for the history of political thought. Numerous political experiments have been marginalized from historical and state-building narratives as the irrelevant work of caudillos, such as the short-lived Rio Grandense Republic in southern Brazil (1836–45). By explaining the Rio Grandense caudillos’ engagement with constitutionalism, this article argues that ‘caudillo’ can be a useful category of analysis if historically contextualized. The article thus reconsiders the history of political thought and state-building in Latin America and beyond in the age of revolutions, suggesting the serious need to scrutinize ‘failed’ states and revolutions. This argument is pursued in three steps. First, the article describes shifting understandings and usages of ‘caudillo’ in nineteenth-century Brazil and neighbouring River Plate states. Second, it analyses the Rio Grandense Republic’s 1842–3 constituent assembly and the novel electoral procedures it employed. Third, it examines the never-promulgated constitutional draft produced by its assemblymen. This constitutional draft is then compared to contemporary River Plate and Brazilian constitutions and its rejection is explained through the assemblymen’s divergent understandings of constitutionalism and democracy.