Defensor pacis

And to understand Marsilius, we need to understand how Aristotle influenced Marsilius' thinking about the state.

It's in Marsilius' works titled Defensor Pacis or Defender of the Peace in 1324, which caused one of the greatest controversies in Catholic history, principally because it called for the separation of church from the state.

In other words, to remove the church from solely interfering in temporal matters concerning society.

The book is profoundly anti-clerical because Marsilius supported the claims of the Holy Roman Emperor Louis V over Pope John XXII.