At 11:00 pm, Mortier notified Napoleon of his plans to retreat to Vendeuvre-sur-Barse and immediately sent orders for his troops to begin evacuating Bar-sur-Aube. The march discipline of the Imperial Guard was so good that the Allies were unaware of their departure until the next morning. Gyulai's corps did not begin the pursuit until the afternoon then it quickly halted at the broken bridge at Spoy. Gyulai mistakenly reported that the French retreated to Châlons-sur-Marne when Mortier was heading for Troyes. The Crown Prince's troops halted and bivouacked in the area. After interrogating his prisoners, Mortier concluded that the Crown Prince's corps numbered 12,000–15,000 men while Gyulai had 30,000. He reported to the emperor that the Allies employed 60 artillery pieces against him including heavy 12-pounder batteries. On 26 January, Napoleon arrived at Châlons-sur-Marne and the Battle of Brienne was fought on 29 January 1814.