II to surrender the three counties ceded to him during the Mongol invasion. On the other hand, Venice occupied Zadar in the summer of 1243. Béla renounced Zadar on 30 June 1244, but Venice acknowledged his claim to one third of the customs revenues of the Dalmatian town. Béla set up a defensive alliance against the Mongols. He married three of his daughters to princes whose countries were also threatened by the Mongols. Rostislav Mikhailovich, a pretender to the Principality of Halych, was the first to marry, in 1243, one of Béla's daughters, Anna. Béla supported his son-in-law to invade Halych in 1245, but Rostislav's opponent, Daniil Romanovich repulsed their attack. On 21 August 1245 Pope Innocent IV freed Béla of the oath of fidelity he had taken to Emperor Frederick during the Mongol invasion. In the following year Duke Frederick II of Austria invaded Hungary. He routed Béla's army in the Battle of the Leitha River on 15 June 1246, but perished in the battlefield. His childless death gave rise to a series of conflicts, because both his niece, Gertrude, and his sister, Margaret, made a claim to Austria and Styria. Béla decided to intervene in the conflict only after the danger of a second Mongol invasion had diminished by the end of the 1240s. In retaliation of a former Austrian incursion into Hungary, Béla made a plundering raid into Austria and Styria in the summer of 1250. In this year he met and concluded a peace treaty with Daniil Romanovich, Prince of Halych in Zólyom (Zvolen, Slovakia). With Béla's mediation, a son of his new ally Roman married Gertrude of Austria. Béla and Daniil Romanovich united their troops and invaded Austria and Moravia in June 1252. After their withdrawal, Ottokar, Margrave of Moravia—who had married Margaret of Austria—invaded and occupied Austria and Styria. In the summer of 1253, Béla launched a campaign against Moravia and laid siege to Olomouc. Daniil Romanovich, Boleslaw the Chaste of Cracow, and Wladislaw of Opole intervened on Béla's behalf, but he lifted the siege by the end of June. Pope Innocent IV mediated a peace treaty, which was signed in Pressburg (Bratislava, Slovakia) on 1 May 1254. In accordance with the treaty, Ottokar, who had in the meantime become King of Bohemia, ceded Styria to Béla. Béla appointed his son-in-law, Rostislav Mikhailovich Ban of Macsó (Mačva, Serbia) in 1254. Rostislav's task was the