Rudolph, so strengthened, besieged Ottokar at the Austrian capital Vienna in 1276. Ottokar was forced to surrender and to renounce all his acquisitions, receiving only Bohemia and Moravia as a fief from King Rudolph. Heavily deprived by this, he was determined to regain his territories and contracted an alliance with the Ascanian Margraves of Brandenburg and the Polish princes. In 1278 he campaigned against Austria, supported by Duke Henry I of Lower Bavaria, who had switched sides. Ottokar first laid siege to the towns of Drosendorf and Laa an der Thaya near the Austrian border, while Rudolph decided to leave Vienna and to face the Bohemian army in an open pitched battle in the Morava basin north of the capital, where the Cuman cavalry of King Ladislaus could easily join his forces.