Thus influenced by the pride of his queen, Cunegunda, Ottocar violated his oath, refused to execute the treaty, imprisoned in a convent the daughter whom Rhodolph had given to his son, and sent a defiant and insulting letter to the emperor.  Rhodolph returned a dignified answer and prepared for war.  Ottocar, now better understanding the power of his foe, made the most formidable preparations for the strife, and soon took the field with an army which he supposed would certainly triumph over any force which Rhodolph could raise.  He even succeeded in drawing Henry of Bavaria into an alliance; and many of the German princes, whom he could not win to his standard, he bribed to neutrality.  Numerous chieftains, lured to his camp by confidence of victory, crowded around him with their followers, from Poland, Bulgaria, Pomerania, Magdeburg, and from the barbaric shores of the Baltic.  Many of the fierce nobles of Hungary had also joined the standard of Ottocar.

Thus suddenly clouds gathered around Rhodolph, and many of his friends despaired of his cause.  He appealed to the princes of the German empire, and but few responded to his call.  His sons-in-law, the Electors of Palatine and of Saxony, ventured not to aid him in an emergence when defeat seemed almost certain, and where all who shared in the defeat would be utterly ruined.  In June, 1275, Ottocar marched from Prague, met his allies at the appointed rendezvous, and threading the defiles of the Bohemian mountains, approached the frontiers of Austria.  Rhodolph was seriously alarmed, for it was evident that the chances of war were against him.  He could not conceal the restlessness and agitation of his spirit as he impatiently awaited the arrival of troops whom he summoned, but who disappointed his hopes.

“I have not one,” he sadly exclaimed, “in whom I can confide, or on whose advice I can depend.”

The citizens of Vienna perceiving that Rhodolph was abandoned by his German allies, and that they could present no effectual resistance to so powerful an army as was approaching, and terrified in view of a siege, and the capture of the city by storm, urged a capitulation, and even begged permission to choose a new sovereign, that they might not be involved in the ruin impending over Rhodolph.  This address roused Rhodolph from his despondency, and inspired him with the energies of despair.  He had succeeded in obtaining a few troops from his provinces in Switzerland.  The Bishop of Basle, who had now become his confessor, came to his aid, at the head of a hundred horsemen, and a body of expert slingers.  Rhodolph, though earnestly advised not to undertake a battle with such desperate odds, marched from Vienna to meet the foe.

Rapidly traversing the southern banks of the Danube to Hamburg, he crossed the river and advanced to Marcheck, on the banks of the Morava.  He was joined by some troops from Styria and Carinthia, and by a strong force led by the King of Hungary.  Emboldened by these accessions, though still far inferior in strength to Ottocar, he pressed on till the two armies faced each other on the plains of Murchfield.  It was the 26th of August, 1278.