Meanwhile, a revived Austria was preparing to strike. The war hawks at the court of Emperor Francis I convinced him to take full advantage of France's preoccupation with Spain. In April 1809 the Austrians opened the campaign without a formal declaration of war and caught the French by surprise. They were too slow to exploit their gains, however, and Napoleon's arrival from Paris finally stabilized the situation. The Austrians were defeated at the Battle of Eckmühl, fled over the Danube, and lost the fortress of Ratisbon, but they still remained a cohesive, fighting force, which meant further campaigning was required to settle the issue. The French captured Vienna and attempted to cross the Danube via Lobau island southeast of the Austrian capital, but they lost the subsequent Battle of Aspern-Essling, the first defeat for the "Grande Armée". A second attempt to cross the river proved more successful in July and set the stage for the two-day Battle of Wagram, where the French emerged victorious, inflicting some 40,000 casualties on the Austrians, but suffering 37,000 themselves. The defeat demoralized the Austrians so heavily that they agreed to an armistice shortly afterwards. This eventually led to the Treaty of Schönbrunn in October 1809. The "Grande Armée" had brought the Fifth Coalition to an end and the Austrian Empire lost three million subjects as a result of the treaty's border changes.