Júlio Prates de Castilhos (Cruz Alta, 29 June 1860 – Porto Alegre, 24 October 1903) was a Brazilian journalist and politician, having been elected Patriarch of Rio Grande do Sul.

[1] He was elected twice as the governor of Rio Grande do Sul and was the principal author of the State Constitution of 1891 and a model for many future politicians of the region.

Less than a year later, the unsuccessful Federalist Revolution began, with one of the rebel force's demands being his removal from power.

Castilhism was a political theory instituted by Júlio de Castilhos in Rio Grande do Sul, having as characteristics the centralization of powers in the Executive, the institution of mechanisms of direct participation, such as plebiscites and popular referendums; the establishment of a modernizing, interventionist and regulating State of the economy, in addition to its intermediary and moralizing role in society.

1231 Duque de Caxias, the last house in which he lived was acquired by the state, following the death of his widow in 1905.