If Tilly had only let the Elector alone, he would probably have had nothing to fear from him for some time to come. But Tilly knew no policy beyond the letter of his instructions. He at once crossed the Saxon frontier. Pappenheim seized Merseburg. Tilly reduced Leipzig to surrender by the threat that he would deal with the city worse than with Magdeburg. The Elector, so long unwilling to draw the sword, was beyond measure angry. He sent speedy couriers to Gustavus, offering his alliance on any terms. [Sidenote: § 5. Union of the Swedes and the Saxons.] Gustavus did not wait for a second bidding. The wish of his heart was at last accomplished. He put his forces at once in motion, bringing the Elector of Brandenburg with him. The Saxon commander was the Lutheran Arnim, the very man who had led Wallenstein's troops to the siege of Stralsund. The Edict of Restitution had taught him that Wallenstein's idea of a Germany united without respect for differences of religion was not to be realized under Ferdinand. He had thrown up his post, and had sought service with John George. Without being in any way a man of commanding ability, he had much experience in war. [Sidenote: § 6. The Saxon troops.] The Saxon soldiers were a splendid sight. New clothed and new armed, they had with them all the pomp and circumstance of glorious war. But they had had no experience of fighting. They were as raw as Wallenstein's troops had been when he first entered the diocese of Halberstadt in 1625. [Sidenote: § 7. The Swedish troops.] The Swedes were a rabble rout to look upon, at least in the eyes of the inexperienced Saxons. Their new allies laughed heartily at their uniforms, ragged with long service and soiled with the dust of the camp and the bivouac. But the war-worn men had confidence in their general, and their general had confidence in them. [Sidenote: § 8. Gustavus as a commander.] Such confidence was based on even better grounds than the confidence of the veterans of the League in Tilly. Tilly was simply an excellent commander of the old Spanish school. He had won his battles by his power of waiting till he was superior in numbers. When the battles came they were what are generally called soldiers' battles. The close-packed columns won their way to victory by sheer push of pike. But Gustavus, like all great commanders, was an innovator in the art of war. To the heavy masses of the enemy he opposed lightness and flexibility. His cannon were more easily moved, his muskets more easily handled. In rapidity of fire he was as superior to the enemy as Frederick the Great with his iron ramrods at Mollwitz, or Moltke with his needle-guns at Sadowa. He had, too, a new method of drill. His troops were drawn up three deep, and were capable of manoeuvering with a precision which might be looked for in vain from the solid columns of the imperialists. SECTION II.--_The Battle of Breitenfeld._ [Sidenote: § 1. Battle of Breitenfeld.]