In June 1520, Pope Leo X wrote the Papal bull Exsurge Domine ("Arise, O Lord"), in which he talked about 41 problems he saw in Martin Luther's Ninety-five Theses and his other works. Because of this, the Holy Roman Emperor told Martin Luther to come to the diet. He promised that he would give Luther safe passage to and from it. The Diet started on 23 January 1521. Martin Luther was told that he had to either take back what he had said or defend it.