Few historical developments are more distinctly traceable or of greater importance than that of the margravate of Brandenburg into the kingdom of Prussia, the principal state of the present German empire. As far back as the tenth century the name Preussen (Prussia) was applied to a region lying east of Brandenburg, which in that century became a German margravate. At that time the inhabitants of Prussia were still heathens. In the thirteenth century they were converted to Christianity, having first been conquered by the Teutonic Knights in "a series of remorseless wars" continued for almost fifty years. German colonization followed the conquest. In 1466 nearly the whole of Prussia was wrested from the Teutonic Knights and annexed to the Polish crown. Soon after the beginning of the Reformation the Teutonic Knights embraced Protestantism and the order became secularized. In 1525 the Knights formally surrendered to King Sigismund of Poland, their late grand master was created duke of Prussia, and this, with other former possessions of the order, was held by him as a vassal of the Polish crown. This relation continued until 1618, when the duchy of Prussia was united with Brandenburg, which had become a German electorate. During the Thirty Years' War the enlarged electorate took little part in affairs, but suffered much from the ravages of the conflict. Under the electorate of George William, who died in 1640, Brandenburg became almost a desert, and in this impoverished condition was left to his son, Frederick William, the "Great Elector," who restored it to prosperity and strengthened its somewhat insecure sovereignty over the duchy of Prussia. The Great Elector died in 1688, and was succeeded by his son, Frederick III of Brandenburg. This Elector, through the series of events narrated by Ranke, became the founder of the Prussian monarchy, and is known in history as Frederick I. He founded the Academy of Sciences in Berlin and the University of Halle. * * * * * Frederick I, the next heir and successor to the "Great Elector," though far inferior to his father in native energy of character, cannot be accused of having flinched from the task imposed on him. Above all, the warlike fame of the Brandenburg troops suffered no diminution under his reign. His army took a very prominent and active part in the most important events of that period. Prince William of Orange might, perhaps, have hesitated whether to try the adventure which made him king of England, had not the Dutch troops, which he was forced to withdraw from the Netherlands for his expedition, been replaced by some from Brandenburg. The fact has indeed been disputed, but on closer investigation its truth has been established, beyond doubt, that many other Brandenburg soldiers in his service and that of his republic followed him to England, where they contributed essentially to his success.