Luther, his cause supported by the German humanists, wins powerful popular support with three celebrated treatises of 1520, in which he states his views.

In “An Open Letter to the Christian Nobility of the German Nation Concerning the Reform of the Christian Estate,” he invites the German princes to take the reform of the church into their own hands.

In “A Prelude Concerning the Babylonian Captivity of the Church,” he attacks the papacy and the current theology of sacraments.

In “On the Freedom of a Christian Man,” he states his position on justification and good works.

The bull of Pope Leo X “Exsurge Domine,” issued on June 15, 1520, threatens Luther and Karlstadt with excommunication, and condemns several of their theses.

Luther has sixty days to recant.