Austrians might retreat along that route. Charles moved his men across the Danube at Regensburg, leaving 6,000 in the fortress to block a pursuit. Lacking time for a siege, Napoleon ordered Marshal Jean Lannes to storm the walls, succeeding at his second attempt and capturing the town by 5 pm in the Battle of Ratisbon. With the Austrian army safely in Bohemia, Napoleon marched towards Vienna. Hiller fought a series of delaying actions, attempting to buy time for the defence of Vienna. After a short fight at Wels on 2 May, Hiller gathered 40,000 troops at the bridge in Ebersberg. Massena launched a costly frontal at the Battle of Ebersberg and captured the position on 3 May, with Hiller withdrawing along the Danube. Charles attempted to move his army to defend Vienna but was outpaced by Napoleon who captured the city on 13 May. The garrison withdrew north of the Danube and destroyed the bridges behind them. Aspern-Essling On 16 May and 17, the main Austrian army under Charles arrived in the Marchfeld, a plain northeast of Vienna just across the Danube that served as a training ground for Austrian military forces. Charles kept most of his forces several miles away from the riverbank, hoping to concentrate them at the point where Napoleon decided to cross. On the 20th, Charles learned from his observers on the Bissam hill that the French were building a bridge at Kaiser-Ebersdorf, just southwest of the Lobau island, that led to the Marchfeld. On 21 May, Charles concluded that the French were crossing at Kaiser-Ebersdorf and ordered a general advance for 98,000 troops and the accompanying 292 guns, organized into five columns. The French bridgehead rested on two villages: Aspern to the west and Essling to the east. Napoleon did not expect to encounter opposition, and the bridges linking the French troops at Aspern-Essling to Lobau were not protected with palisades, making them vulnerable to Austrian barges that had been set ablaze. The Battle of Aspern-Essling started at 2:30 pm on 21 May. The initial attacks were made by the first three columns on Aspern and the Gemeinde Au woods but were poorly coordinated and failed. Later assaults succeeded in taking and holding the western portion of the village. The Austrians did not attack Essling until 6 pm because the fourth and fifth columns had longer marching routes. The French successfully repulsed the attacks against