He devoted himself to the military career, which did not take long to detest, longing for the contemplative life. He fought as a captain in the Battle of St. Quentin and, as a general of artillery, in the Tercios of Flanders in the service of Fernando Álvarez de Toledo y Pimentel, the Duke of Alba, During the Siege of Haarlem he was wounded in one foot by an arquebus shot.