Gunpowder was now coming into use as one of the most efficient engines of destruction, and was working great changes in the science of war. It became necessary to have troops drilled to the use of cannon and muskets. The baron could no longer summon his vassals, at the moment, to abandon the plow, and seize pike and saber for battle, where the strong arm only was needed. Disciplined troops were needed, who could sweep the field with well-aimed bullets, and crumble walls with shot and shells. This led to the establishment of standing armies, and gave the great powers an immense advantage over their weaker neighbors. The invention of printing, also, which began to be operative about the middle of the fifteenth century, rapidly changed, by the diffusion of intelligence, the state of society, hitherto so barbarous. The learned men of Greece, driven from their country by the Turkish invasion, were scattered over Europe, and contributed not a little to the extension of the love of letters. The discovery of the mariner's compass and improvements in nautical astronomy, also opened new sources of knowledge and of wealth, and the human mind all over Europe commenced a new start in the career of civilization. Men of letters began to share in those honors which heretofore had belonged exclusively to men of war; and the arts of peace began to claim consideration with those who had been accustomed to respect only the science of destruction. Maximilian was at Innspruck when he received intelligence of the death of his father. He commenced his reign with an act of rigor which was characteristic of his whole career. A horde of Turks had penetrated Styria and Carniola, laying every thing waste before them as far as Carniola. Maximilian, sounding the alarm, inspired his countrymen with the same energy which animated his own breast. Fifteen thousand men rallied at the blast of his bugles. Instead of intrusting the command of them to his generals, he placed himself at their head, and made so fierce an onset upon the invaders, that they precipitately fled. Maximilian returned at the head of his troops triumphant to Vienna, where he was received with acclamations such as had seldom resounded in the metropolis. He was hailed as the deliverer of his country, and at once rose to the highest position in the esteem and affection of the Austrians. Maximilian had encountered innumerable difficulties in Burgundy, and was not unwilling to escape from the vexations and cares of that distant dukedom, by surrendering its government to his son Philip, who was now sixteen years of age, and whom the Burgundians claimed to be their ruler as the heir of Mary. The Swiss estates were also sundered from Austrian dominion, and, uniting with the Swiss confederacy, were no longer subject to the house of Hapsburg. Thus Maximilian had the Austrian estates upon the Danube only, as the nucleus of the empire he was ambitious of establishing.