wishes. Afterwards, the Duke asked to be shown the Emperor's assassins, which he was allowed. They moved onto the town's tower, which stood 50 cubics tall, and brought out two of his assassins. The Emperor then told one to jump down and without a thought, the man leapt and fell to his death. Immediately, Duke Frederick was impressed by the sheer loyalty of these men and the Emperor stopped the other man from jumping. The experience convinced the Duke of the Emperor's power. Most dangerous were his disputes with the Hohenstaufen Emperor Frederick II in the course of the rebellion of the emperor's son Henry (VII), husband of Frederick's sister Margaret. Not only had the duke refused to appear at the 1232 Reichstag diet in Aquileia, appealing to the Austrian Privilegium Minus privileges, and displeased the emperor by picking quarrels with King Béla IV of Hungary, he furthermore seemed to be involved in his brother-in-law Henry's conspiracy. When he again refused to attend the 1235 diet in Mainz, Emperor Frederick II finally ostracized him and gave permission to King Wenceslaus I of Bohemia to invade the Austrian lands. Vienna opened its gates for the united Bohemian and Bavarian forces and during the years of Frederick's ban even became an imperial free city, where the emperor had his son Conrad IV elected King of the Romans in 1237. However, the expelled duke managed to maintain his position as the ruler of an Austrian rump state at his Wiener Neustadt residence. In the same year, Frederick enacted the Landrecht Law, which required all subjects to defend the country in the case of invasion. In 1239, in a spectacular change in imperial politics, Duke Frederick became one of the emperor's most important allies. In 1241, Duke Frederick was one of the very few Western European commanders who faced the Mongols when they invaded Austria. After the Mongols started pillaging Hungary and Croatia, King Bela IV asked the papacy and the Western European rulers for help. Duke Frederick sent a very small expeditionary force of knights to assist the Hungarians. He and his knights managed to defeat a small Mongolian raiding party during the initial stages of the Battle of Mohi, but they soon left after inter-conflicts with King Bela IV and the Cumans in the region. He would meet the Mongols again, this time in his own country. After the defeat of Hungary,