  Descartes left Breda in 1619 to join the Catholic army of Maximilian I (Duke of Bavaria and ally of France). The war concerned the authority of Ferdinand V, a Catholic, who had been crowned emperor of the Holy Roman Empire in September. Descartes attended the coronation and was returning to the army when winter caught him in the small town of Ulm (or perhaps Neuburg), not far from Munich. On the night of November 10, 1619, Descartes had three dreams that seemed to provide him with a mission in life. The dreams themselves are interesting and complex (see Sebba 1987). Descartes took from them the message that he should set out to reform all knowledge. He decided to begin with philosophy, since the principles of the other sciences must be derived from it (6:21–2).