The siege of Dresden (10 October-11 November 1813) was triggered by Napoleon's decision to leave a garrison in the city in the days before the battle of Leipzig, exposing it to an inevitable attack and leaving it trapped after his defeat.
In late September Napoleon decided to abandon the area to the east of the Elbe, and attempt to catch one of the Allied armies as they attempted to either cross the river or the Bohemian mountains. Dresden, on the Elbe, remained a key position while the line of the river remained in French hands, but on 3 October Blücher fought his way across the Elbe at Wartenberg, to the north-west of Dresden, and moved west to join Bernadotte. The river line was broken, and all of Napoleon's attention turned to the area around Leipzig.
St. Cyr's XIV Corps and Lobau's I Corps were left in the Dresden area as Napoleon began an attempt to catch Blücher north of Leipzig. Napoleon couldn’t make up his mind what to do with them. If it came to a general battle then he would need every man, but he also didn't want to abandon Dresden, the capital of Saxony, his main remaining Ally in Germany. At midnight on 6-7 October Napoleon decided to abandon Dresden, and use St. Cyr and Lobau in the pursuit of Blücher and Bernadotte. By 1pm on 7 October Napoleon had changed his mind, and St. Cyr and Lobau were ordered to defend Dresden. This was a crucial mistake. Over the next few days the Allies began a blockade of Dresden, and Napoleon would sorely miss these two corps during the battle of Leipzig.
Colloredo's advance guard reached Zehista, south of Pirna (east of Dresden), on 8 October. On the same day Bubna, who had been left behind by Blücher, captured the French bridgehead opposite Pirna.
On 10 October Bennigsen left 20,000 men under Osterman-Tolstoy to blockade Dresden, and took the rest of this men towards Leipzig.
On 17 October St Cyr attacked the Allied lines around Hacknitz. He formed his garrison into six divisions, and used four of them for the attack. Two divisions, under Gerard, attacked the Russians in the front, and the other two hit their flanks. The Russians were forced out of their redoubts, and the French captured 1,200 prisoners, 10 guns and 20 caissons. The Russians retreated south to Berggieshübel, where they met up with 10,000 Austrian reinforcements under General Chasteler. St. Cyr retreated into Dresden.
After the battle of Leipzig Schwarzenberg sent Klenau's corps to besiege Dresden. This force arrived outside the city on 26 October. St Cyr was forced to pull his garrison inside the fortifications which protected the suburbs. However he didn’t have many supplies within the city – the area around Dresden had been at the centre of the war since the spring, and there was very little food to be had in the surrounding area.
On 5 November St Cyr decided to try and break through the siege lines on the right bank of the river, and escape via Torgau and Wittemberg. He would join up with the garrisons of those places and then attempt to retreat back to France. However the combined forces of Tolstoy and Klenau were too strong, and the attempt failed. St. Cyr was forced to retreat back into the walls.
Eventually a shortage of food forced him to surrender on terms on 11 November, by which time Dresden was the last French foothold in Saxony. The Allied negotiators agreed to allow St Cyr's men to return to France as long as they promised not to fight again in the current war.
St. Cyr's men were already on the road when news arrived that Schwarzenberg had refused to ratify the agreement. The Allies offered to allow St Cyr to return to Dresden, but only with the same supplies as at his surrender. St Cyr realised that this would have been a pointless gesture, and his army went into captivity. St Cyr himself remained a captive at Karlsbad until Napoleon's first abdication.