First day Napoleon had not anticipated a significant engagement on the northern bank. The significant deployment of light cavalry at the head of the crossing schedule suggests that he still anticipated the necessity to locate Charles' army. At 4:00 p.m. on the 21st, Napoleon convened a meeting with his senior military officers to review the latest intelligence and plan the next steps. Despite the expectation that Bessières' advanced cavalry patrols would have discovered the presence of the main Austrian army so close to the bridgehead, they sent back no such information. This suggests that the French reconnoitering cavalry proved ineffective on this occasion. As there were no reports of the enemy, Lannes stated that he believed the army would encounter no more than 8,000 Austrians on the 21st, at the very outside. Only the cautious Masséna made an estimation that the enemy might already be nearby in force, but this was not agreed with by the others. At approximately 1:00 p.m., the leading elements of the Austrian 1st Corps drove Molitor's outposts back into Aspern. The French were caught off-guard; the attack was hidden by the combination of a low ridge and a convenient dust storm until the last moment. However, Molitor was able to repel the initial attack and gain sufficient time to bring all four of his regiments into the town. Despite repeated Austrian attacks throughout the afternoon, the French defence held firm. However, by 5:00 p.m. the Austrian forces had formed a half-circle around Aspern, and Archduke Charles ordered a general assault. Molitor was now facing significant challenges in maintaining his position, with the enemy launching simultaneous attacks from three directions. In the hours that followed, Aspern changed hands no less than six times. However, Molitor was determined not to concede defeat and continued to hold his position until he could be reinforced by Legrand and Carra St. Cyr. This enabled the vital bridge to be opened to traffic once more. Meanwhile, in a strategic centerpiece, the 7,000 sabers of Bessières engaged in a prolonged battle against Austrian cavalry and neighboring corps. The garrison at Essling was holding its own on the extreme right. Here, the French forces were only effectively attacked by Rosenberg's 4th Corps from 6:00 p.m. onwards. Due to Lannes' strategic deployment of Boudet's troops positioned within the town, the French successfully repulsed three successive Austrian attacks, maintaining control of their position and preventing significant losses. Just before 7:00 p.m., the last new personnel arrived on the scene. St. Germain's brigade from Nansouty's division and St. Sulpice's cuirassiers were present for Bessiéres' final assault on the enemy centre, but there were no significant outcomes. With the onset of darkness, the majority of combat ceased, and the two armies settled into a state of relative calm, with the exception of the ongoing engagement at Aspern, where a narrow distance separated the French and Austrian forces. At his new headquarters in
Breitensee, Archduke Charles was engaged in planning the next day's operations. Meanwhile, on the nearby island of Lobau, Napoleon was sending urgent messages to Davout in Vienna and mobilising all available troops in the bridgehead. The bridge remained open for the majority of the night, allowing Lannes' command, comprising St. Hilaire's division and Oudinot's corps of grenadiers (Tharreau and Claparéde's divisions), to safely reach the bridgehead by 4:00 a.m. This contingent was accompanied by additional cavalry and artillery units. The new troops were immediately deployed to secure the central sector of the position, while Bessiéres' cavalry was redeployed to a local reserve position. Boudet's troops were still in control of Essling, with a contingent on their right occupying the open ground. On the left flank, Aspern and its surrounding area were under the control of Legrand and Carra St. Cyr. However, Molitor's depleted regiments, which had been the primary focus of the previous day's fighting, were relocated to a reserve position to the south. In addition, two divisions of the Guard were positioned to defend the bridgehead, and General Demont's division was preparing to cross from Lobau. This brought the French forces to around 50,000 infantry, 12,000 cavalry and 144 guns. They were facing over 100,000 Austrian troops supported by at least 260 artillery pieces.
Second day Despite the cessation of hostilities in Aspern earlier that evening, sporadic fighting continued throughout the night. At approximately 5:00 a.m., the Austrian 1st and 5th Corps initiated a new full-scale assault on the town and the nearby wooded area known as Gemeinde-Au. This was conducted under cover of darkness and a thick mist. The fortunes of the struggle fluctuated, but a particularly successful counterattack by Massena at approximately 7:00 a.m. resulted in the French recapturing the entirety of Aspern. Meanwhile, Dedovich and Rosenberg leading the fourth and fifth columns, respectively launched a new attack on Essling. Despite making some progress, they were unable to gain the upper hand and were held back by Boudet's forces. This meant that Napoleon was in a position to contemplate a breakout from the bridgehead. There is a strong possibility that he had intended Davout to provide support for this operation, but due to a lack of available bridges, Davout's corps was not involved in the battle. Notwithstanding this, Napoleon remained confident and ordered an attack from the centre of his position, perhaps with the expectation that Davout would still arrive. Shortly after 7:00 a.m. Lannes' corps began to advance in echelon, with Saint-Hilaire leading on the right and Oudinot following in the centre and on the left with Claparéde's and Tharreau's divisions. They marched into a sustained bombardment, but the Austrians at the front wavered, forcing Charles to send his reserve grenadier divisions forward, which halted the French. Napoleon then tried to salvage the situation with a series of cavalry chargers under Bessiéres, but they too were driven back. At this point, Napoleon was becoming seriously concerned by reports from another quarter. Shortly after eight o'clock he learned that the bridge had broken down again, meaning that Davout's corps could not cross. This, together with the fact that Lannes failed to bring the Austrian center down, left Napoleon with no alternative but to order a gradual withdrawal to Aspern and Essling. When Archduke Charles heard of the new collapse of the bridge at 10 a.m., he ordered his troops to attack again. All the while, fighting raged on the flanks. The first and second Austrian columns attacked Aspern again and another desperate battle ensued until an artillery barrage drove the defenders back. Shortly after 1:00 p.m., with no reserves left and exhausted after a day of almost non-stop fighting, the French finally abandoned the village. At approximately two in the afternoon, Charles initiated a strategic withdrawal of his units, positioning approximately 150 cannons to engage the French centre. During this intense period of bombardment, Lannes was struck by a cannonball that resulted in a fatal injury to his leg. Napoleon was also subject to enemy fire and, at the insistence of his personal guards, withdrew to the Lobau. Subsequently, Rosenberg's IV Corps, supported by Merville's grenadiers, led by Charles, forced Boudet out of Essling. However, the general and a few hundred Grenadiers were able to hold out in the granary. It was imperative that Essling be held, and thus Napoleon dispatched General Mouton with some Young Guard battalions to retake the village. Mouton advanced into Essling but was at risk of being isolated by Austrian reinforcements. General Rapp was dispatched with two additional battalions of
Middle Guard Fusilier Grenadiers to reinforce Mouton. Rapp advised Mouton to disregard Napoleon's orders and launch a counterattack against the Austrian troops in Essling. The French battalions advanced, charged, repulsed and dispersed the enemy at the point of the bayonet. Rosenberg lost his nerve and fell back towards Gross-Enzersdorf. It was evident that Napoleon's position was untenable. With no reinforcements or ammunition, his only viable option was to abandon the bridgehead and retreat to Lobau, where he could await the reestablishment of the bridge. Deciding that enough had been achieved Charles did not pursue. The decision not to pursue allowed Napoleon to withdraw his army from the north bank of the Danube, and by 23 May the last French troops had left. ==Aftermath==