At the time of the battle Napoleon was in possession of Vienna, the bridges over the Danube had been broken, and the Archduke's army was near the Bisamberg, a hill near Korneuburg, on the left bank of the river. The French wanted to cross the Danube. A first crossing attempt on the Schwarze Lackenau on 13 May was repulsed with some 700 French losses. Lobau, one of the numerous islands that divided the river into minor channels, was selected as the next point of crossing. Careful preparations were made, and on the night of 19–20 May the French bridged all the channels on the right bank to Lobau and occupied the island. By the evening of the 20th many men had been collected there and the last arm of the Danube, between Lobau and the left bank, had been bridged. Masséna's corps at once crossed to the left bank and dislodged the Austrian outposts. Undeterred by the news of heavy attacks on his rear from Tyrol and from Bohemia, Napoleon ferried all available troops to the bridges, and by daybreak on the 21st, 40,000 men were collected on the Marchfeld, the broad plain of the left bank, which was also to be the scene of the Battle of Wagram.