Most of the great captains of an early day thus signalized their progress by some improvement in the equipment of their infantry. One of the most formidable enemies of Spanish power, Maurice of Nassau, a skilful engineer and tactician, was the first to array infantry in such a manner as to combine the simultaneous use of the musket and the pike. Before his time, fire-arms had been used only for skirmishing service; he commenced to use them in line. This reform was, however, only foreshadowed, as it were, by the Dutch General; it was reserved for Gustavus Adolphus to complete it. While he was executing a series of military operations such as the world had not beheld since the days of Cæsar, he was also creating a movable artillery, and giving to the fire of his infantry an efficacy which had not been attained before. For the heavy machines of war which were drawn by oxen to the field of battle, and which remained there motionless and paralyzed by the slightest movements of the contending armies, he substituted light cannon drawn by horses and following up all the manoeuvres of either cavalry or foot. He had found the infantry formed in dense battalions. His system arranged it in long continuous lines in which each rank of musketeers was sustained by several ranks of pikemen, so that his array, thus distributed, should present to the enemy a front bristling with steel, while, at the same time, it could cover a large space of ground with its discharge of lead. Attentive to all kinds of detail, he also gave his soldiers the cartouch-box and knapsack instead of the cumbersome apparatus to which they had been accustomed. In fact, Gustavus Adolphus was the founder of the modern science of battle. In strategy and the grand combinations of warfare, he was the disciple and rival of the ancient masters; for, even if this "divine portion" of the military art be inaccessible to the vast number of its votaries, and if history can easily enumerate those who were capable of comprehending it, and, more especially, of applying it, its rules and principles have, nevertheless, been by no means the same in all ages. On the contrary, the invention of fire-arms demanded an entirely new system of tactics, and this the Swedish hero introduced.