Of the territories by which the original Mark of Brandenburg had been augmented, two were of special importance. In 1525 East Prussia had been acquired. This province, which throughout this book will be called by its German name of Ost-Preussen, was richer by far than the Mark, the kernel of the Hohenzollern possessions. It had an important city, Königsberg, for its capital and a coast-line on the Baltic. It constituted the domain of the old Order of Teutonic Knights, permanent crusaders whose task had been to spread the faith and civilisation of their fatherland among the heathen Slavs. But the Baltic lands had all submitted to the Cross, and the Knights became in their turn the objects of a religious mission. Early in the sixteenth century, the doctrines of the Reformation penetrated the minds of their High Master, Albert of Hohenzollern. He turned for counsel to Luther himself. In a celibate Order which had no more heathen to convert, the husband of the nun Catherine Bora could see only a standing defiance of the laws of nature and of God. By his advice Ost-Preussen was “secularised,” that is, taken from the service of religion to form a Hohenzollern estate, and in time (1618), though still submissive to the suzerainty of Poland, it was added to the main body of the Electoral dominions. The Hohenzollerns thus became distinguished from the mass of German princes by ruling territories to which the Empire had never possessed any claim. Ost-Preussen was to them on a small scale what England became in 1688 to the House of Orange, or in 1714 to the House of Hanover. Their policy acquired a new breadth and a new weight. Hitherto provincial, it became more and more cosmopolitan, and commerce with the Baltic lands and England began to hint to the lord of Pillau and Memel that his future lay upon the water. A makeweight to Ost-Preussen, which would prevent the centre of gravity of the Hohenzollern lands from shifting eastwards, was found in 1609, when the family inherited Cleves, Mark, and Ravensberg in Western Germany. This acquisition, made on the very eve of the Thirty Years’ War, was accompanied in 1613 by the conversion of the Elector, John Sigismund, from the Lutheranism which his grandfather, Joachim II., had established in 1539 to the sterner and more militant creed of Calvin. This meant that at the very moment when all Germany was taking up arms for the greatest religious war of modern times, the court and people of Brandenburg were hopelessly at variance with one another. A Calvinist prince ruled a Lutheran people, and the new Elector, George William (1619–1640), “of Christ-mild memory” but the weakest of his line, proved to be a puppet in the hands of Schwarzenburg, his Romanist prime-minister. Under such guidance did Brandenburg, ill-knit and ill-armed, become the battle-ground between Swede and Hapsburg in their struggle for faith and empire.