While the two armies continued in this situation, some traitors repaired to the camp of-Rudolph and proposed to assassinate Ottocar, but Rudolph, with his characteristic magnanimity, rejecting this offer, apprised Ottocar of the danger with which he was threatened, and made overtures of reconciliation.  The King of Bohemia, confident in the superiority of his force, deemed the intelligence a fabrication and the proposals of Rudolph a proof of weakness, and disdainfully refused to listen to any negotiation.

Finding all hopes of accommodation frustrated, Rudolph prepared for a conflict, in which, like Caesar, he was not to fight for victory alone, but for life.  At the dawn of day, August 26, 1278, his army was drawn up, crossed the rivulet which gives name to Weidendorf, and approached the camp of Ottocar.  He ordered his troops to advance in a crescent, and attack at the same time both flanks and the front of the enemy, and then, turning to his soldiers, exhorted them to avenge the violation of the most solemn compacts and the insulted majesty of the empire, and by the efforts of that day to put an end to the tyranny, the horrors, and the massacres to which they had been so long exposed.  He had scarcely finished before the troops rushed to the charge, and a bloody conflict ensued, in which both parties fought with all the fury that the presence and exertions of their sovereigns or the magnitude of the cause in which they were engaged could inspire.  At length the imperial troops gained the advantage, but in the very moment of victory the life of him on whom all depended was exposed to the most imminent danger.

Several knights of superior strength and courage, animated by the rewards and promises of Ottocar, had confederated either to kill or take the King of the Romans.  They rushed forward to the place where Rudolph, riding among the foremost ranks, was encouraging and leading his troops, and Herbot of Fullenstein, a Polish knight, giving spurs to his horse, made the first charge.  Rudolph, accustomed to this species of combat, eluded the stroke, and, piercing his antagonist under his beaver, threw him dead to the ground.  The rest followed the example of the Polish warrior, but were all slain, except Valens, a Thuringian knight of gigantic stature and strength, who, reaching the person of Rudolph, pierced his horse in the shoulder, and threw him wounded to the ground.  The helmet of the King was beaten off by the shock, and being unable to rise under the weight of his armor he covered his head with his shield, till he was rescued by Berchtold Capillar, the commander of the corps of reserve, who, cutting his way through the enemy, flew to his assistance.  Rudolph mounted another horse, and, heading the corps of reserve, renewed the charge with fresh courage, and his troops, animated by his presence and exertions, completed the victory.