Luther made his pronouncements from Wartburg in the context of rapid developments at Wittenberg, of which he was kept fully informed. Andreas Karlstadt, supported by the ex-Augustinian Gabriel Zwilling, embarked on a radical programme of reform there in June 1521, exceeding anything envisaged by Luther. The reforms provoked disturbances, including a revolt by the Augustinian friars 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. Wittenberg became even more volatile after Christmas when a band of visionary zealots, the so-called Zwickau prophets, arrived, preaching revolutionary doctrines such as the equality of man, adult baptism, and Christ's imminent return. When the town council asked Luther to return, he decided it was his duty to act.