In spite of the coldness of the king, Arnheim persisted, for he had been ordered to secure the assistance of the king of Sweden at any price. Arnheim pressed him to name any conditions, saying: "I shall see they are accepted." At last Gustavus said: "I require that the Elector shall cede to me the fortress of Wittenberg, deliver to me his eldest son as hostage, furnish my troops with three months' pay, and deliver up to me the traitors among his ministry."
"Not Wittenberg alone," said the Elector, when he had read the message, "but Torgau and all Saxony shall be open to him, my whole family shall be hostages, and if that is not enough, I will place myself in his hands. Return and inform him I am ready to deliver to him any traitors he shall name, to furnish his army with any money he requires, and to venture my life and fortune in the good cause."
The king had only been testing him, and now, believing in the sincerity of the Elector's intentions, he very much modified his demands. "The distrust," said the king, "which he had shown me when advancing to the relief of Magdeburg, had made me distrustful; his present confidence demands a return. I shall be satisfied if he grants my army one month's pay, and even for this advance I hope to indemnify him."
On September 1st, 1631, the princes signed an alliance, and on September 5th the Saxon army joined that of Sweden. Tilly had encamped near Leipzig and had fired on the city. He said to his army, jubilant with the hope of plunder, "Hitherto heretics have never gained a victory in a pitched battle." Gustavus took the opposite course. He assembled all his field officers about him the evening before the battle, and said: "I neither despise our enemies, nor represent the affair as more easy than it is. I do not conceal it; we have before us an experienced, powerful, victorious enemy, who has hitherto, during his long wars, been always triumphant. But the more celebrated this enemy is the greater will be the renown which we shall obtain by conquering him. All honor, praise and glory which our adversaries have acquired during so many years can, with the help of God, be our own within twenty-four hours. On our side is the right. We do not contend for temporal goods, but for the glory and for the word of God; for the true religion, which alone is able to save, hitherto grievously oppressed by the Catholics and which they now intend to entirely destroy. We must not doubt that Almighty God, who, in spite of all resistance, has led us safely through all kinds of dangers, will now grant us His efficient assistance." Then he rode through his camp, cheering with kind words his soldiers, and making each feel that he was indeed an important factor for his king, for his country and for his religion.
Munro says the Elector of Saxony and his troops looked as if they were there to have pictures or portraits taken, while the Swedes, who had been on a long march and had slept in a dusty field, looked like servants, and they both looked tame beside the besilvered, begilded and beplumed Imperialists. The Swedish horses looked like ponies beside the gigantic German chargers. The king had on a plain buff-colored suit, a gray hat, with a green plume.
In the meantime, Tilly pushed close to Leipzig and promised to leave it like Magdeburg if it did not yield. But conditions were not the same. On September 4th the bombardment began. On the 6th the city sent to offer Tilly a large sum of money in ransom, then capitulated on condition that the Protestant religion should not be suppressed and the garrison be permitted to march out with honors of war. Tilly put three thousand soldiers in the city and determined to await the Swedes and Saxons, with his back protected by the city.
On September 9th, 1631, the hostile armies were in sight of each other, between Breitenfield and Leipzig, and here the great battle of the war was to be fought. It was not Tilly and Gustavus Adolphus, but the two systems of religion which that day stood face to face. The Swedish and Saxon army amounted to about thirty-five thousand men, and the Emperor and the Catholic League had about the same number. But if all the millions which each side represented had all been present, the battle would not have been more representative, more decisive, nor more important.
Tilly's usual confidence had deserted him, and he said afterward that he was forced into battle by his own subordinate, General Pappenheim.
The battle began with two hours of cannonading, the wind, being from the west, blew the smoke, the dust from the plains and from a plowed field, into the faces of the Swedes. The king quickly moved his forces to the north, and Tilly left his position and attacked the Swedes, but their fire was so galling that he moved to the right and attacked the Saxons with such tremendous impetuosity that their line was broken and the whole army thrown into confusion. The Elector himself retired to Eilenberg, but in spite of his defection, a few of his best regiments held their ground and saved the good name of Saxony.
Pappenheim, the Phil Sheridan of the Imperial army, threw his best cavalry regiments against the Swedes, where the king of Sweden himself commanded. Seven times did Pappenheim make his swift charge, seven times repulsed. He left most of his men on the field, which he abandoned to his conquerors. In the meantime, Tilly, having routed the remainder of the Saxons, attacked with his triumphant troops the left wing of the Swedes, commanded by General Gustavus Horn. The Swedes made a gallant resistance, until the king, with the troops who had driven Pappenheim from the field, came to terminate the battle. After driving Tilly and his troops out of the way, Gustavus reached the eminence on which the Imperial artillery had been placed, and he turned on the Imperialists the full destructive play of their own artillery. Tilly forced a retreat through the midst of his conquerors, and left only four veteran regiments to meet Gustavus and his victors.