In Wittenberg, Andreas Karlstadt, later supported by the ex-Augustinian Gabriel Zwilling, enacted a divisive programme of reform which exceeded anything envisaged by Luther and provoked disturbances, including a revolt by the Augustinian monks against their prior, the smashing of statues and images in churches, and denunciations of the magistracy. After secretly visiting Wittenberg in early December 1521, Luther wrote "A Sincere Admonition by Martin Luther to All Christians to Guard Against Insurrection and Rebellion"; but Wittenberg became more volatile after Christmas when a band of visionary zealots, the so-called Zwickau prophets, arrived preaching the equality of man, adult baptism, Christ's imminent return, and other revolutionary doctrines. Luther decided it was time to act.